Piezoelectric vibration angular velocity meter and camera using the same

ABSTRACT

When a power switch is turned on, first and second analog switches are turned on while a third analog switch is turned off. Accordingly, at the time of starting, a forced excitation driving circuit supplies to a vibrator an oscillation output pulse which is substantially at the resonance frequency of the vibrator, thereby forcibly driving the vibrator in an excitation manner. Thereafter, when the vibrator substantially attains its stationary state and thereby the charged voltage of a capacitor reaches a threshold value of an inverter, the first and second analog switches are turned off while the third analog switch is turned on. Accordingly, the output of a self-excitation circuit is supplied to the electrode of the vibrator so as to vibrate the vibrator in a self-excitation manner.

RELATED APPLICATIONS

This is a continuation-in-part application of application Ser. No.08/520,912 filed on Aug. 30, 1995, now pending.More than one reissueapplication has been filed for the reissue of Ser. No. 08/661,788, filedJun. 13, 1996, U.S. Pat. No. 5,794,080, which is a Continuation-In-Partof Ser. No. 08/520,912 filed Aug. 30, 1995, abandoned. The reissueapplications are application Ser. No. 11/441,460 (the presentapplication), filed May 26, 2006 and Ser. No. 12/687,757, filed Jan. 14,2010, which is a continuation reissue application of parent reissueapplication Ser. No. 11/441,460.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an angular velocity meter using apiezoelectric element and a camera using the meter and, moreparticularly, to a camera which prevents a camera shake.

2. Related Background Art

A conventional piezoelectric vibration angular velocity meter isdisclosed in Japanese Patent Laid-Open No. 3-150914.

SUMMARY OF THE INVENTION

The piezoelectric angular velocity meters of the present invention canbe classified into bimorph and unimorph piezoelectric angular velocitymeters.

A bimorph piezoelectric angular velocity meter includes a piezoelectricelement. This piezoelectric element includes a first piezoelectricelement and a second piezoelectric element bonded to the firstpiezoelectric element.

The second piezoelectric element includes a second member made of apiezoelectric crystal, and upper- and lower-surface electrodessandwiching the second member.

The first piezoelectric element is fixed to the upper-surface electrodeof the second piezoelectric element with an adhesive. The firstpiezoelectric element includes a first member made of a piezoelectriccrystal, upper-surface electrodes, and a lower-surface electrode. Theupper- and lower-surface electrodes sandwich the first member. Anadhesive is interposed between the lower-surface electrode of the firstmember and the upper-surface electrode of the second member. Theupper-surface electrodes include a left electrode, a right electrode,and a middle electrode located between the left and right electrodes.These electrodes extend along the longitudinal direction of thepiezoelectric element.

The first and second members are made of PZT. Each electrode is made ofa silver paste.

When an AC voltage is applied between the upper- and lower-surfaceelectrodes of the second piezoelectric element, the piezoelectric issubjected to element self-excited vibration. Since the first and secondpiezoelectric elements are bonded to each other, the first piezoelectricelement also vibrates at this time. The piezoelectric element deflectsin the direction of thickness of the piezoelectric element.

When the piezoelectric element is caused to vibrate without being fixedanywhere, i.e., when the piezoelectric element is vibrated in anonrestraint state, the piezoelectric element (vibrator) vibrates on twonodes.

This piezoelectric angular velocity meter further includes a substrate.Two support portions are interposed between the substrate and the secondpiezoelectric element. The two support members are interposed betweenthe piezoelectric element and the substrate at positions correspondingto the two nodes of vibration.

Assume that when the piezoelectric element is vibrated, thepiezoelectric element deflects such that the central position of theelement moves at a velocity V. At this time, when this piezoelectricelement rotates about the central axis along the longitudinal directionof the piezoelectric element, a Coriolis force is generated in adirection (lateral direction) perpendicular to both the longitudinaldirection and the direction of thickness of the piezoelectric element.As a result, the piezoelectric element deflects in the lateraldirection.

The deflection amount of the piezoelectric element in the lateraldirection corresponds to the rotational angular velocity of thepiezoelectric element. This deflection amount can be measured bydetecting the difference between voltage signals output from the leftand right electrodes of the second piezoelectric element. Ideally, thedeflection amount of the middle electrode in the direction of thicknessdoes not change even if the piezoelectric element deflects in thelateral direction. In practice, however, the deflection amount of themiddle electrode in the direction of thickness slightly changes. If thedeflection amount in the direction of thickness changes, an accurateangular velocity cannot be detected. For this reason, the amplitude ofan AC voltage to be applied to the piezoelectric element is controlledby an automatic level control circuit such that the deflection amount(amplitude) of the middle electrode of the piezoelectric element in thedirection of thickness is kept constant.

This piezoelectric angular velocity meter can be applied to a camera.The camera includes a motor for moving a lens. The motor is controlledby a central processing unit (CPU).

The CPU controls the motor not to change the positions of a film and theoptical axis of the lens in the camera on the basis of an angularvelocity detected by the piezoelectric angular velocity meter, therebycausing the motor to move the lens.

A unimorph piezoelectric angular velocity meter does not have a firstmember. In a bimorph piezoelectric angular velocity meter, thepiezoelectric element may be cantilevered.

An angular velocity meter according to the present invention comprises avibrator and a self-excitation driving circuit for driving said vibratorin a self-excitation manner, and the self-excitation driving circuitcomprises: a converting means for converting a first sine wave voltageindicative of a state of vibration of the vibrator into a square wavevoltage which becomes a first predetermined level when the first squaresine wave voltage is greater than a predetermined reference level whilebecoming a second predetermined level when the first square sine wavevoltage is smaller than the predetermined reference level; a filter forfiltering a second sine wave voltage, which has a frequency identical toa frequency of the first sine wave voltage, from the square wavevoltage; and a phase shifter for adjusting a phase of the second sinewave voltage, which has been filtered by the filter, such that anamplitude of vibration of the vibrator is substantially maximized.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will beapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a piezoelectric element according to anembodiment of the present invention;

FIG. 2 is a longitudinal sectional view taken along the directionindicated by an arrow Z in FIG. 1 illustrating the piezoelectricelement;

FIG. 3A is a perspective view showing the piezoelectric element in FIG.1, a circuit for driving the piezoelectric element, and a case forhousing them;

FIG. 3B is a perspective view of a piezoelectric angular velocity meter;

FIG. 4A is a perspective view of a camera using the piezoelectricangular velocity meter in FIG. 3B;

FIGS. 4B to 4D are views showing control of the lens of the camera;

FIG. 5 is a block diagram showing a piezoelectric element and a circuitfor driving it;

FIGS. 6A and 6B are timing charts for explaining the operation of thecircuit in FIG. 5;

FIG. 7 is a block diagram showing a camera system for moving the lens inaccordance with a signal output from the piezoelectric angular velocitymeter;

FIG. 8A is a perspective view of the piezoelectric element in FIG. 1;

FIG. 8B is a sectional view taken along the direction indicated by anarrow Z in FIG. 8A illustrating the piezoelectric element;

FIGS. 9A to 9C are views for explaining the operation of thepiezoelectric element;

FIG. 9D is a sectional view showing the piezoelectric element fixed to asubstrate via support members;

FIG. 10A is a plan view of a piezoelectric element;

FIG. 10B is a sectional view taken along the direction indicated byarrows Z in FIG. 10A illustrating the element;

FIG. 10C is a plan view of a piezoelectric element;

FIG. 10D is a sectional view taken along the direction indicated byarrows Z in FIG. 10C illustrating the element;

FIG. 10E is a plan view of a piezoelectric element;

FIG. 10F is a sectional view taken along the direction indicated byarrows Z in FIG. 10E illustrating the element;

FIG. 10G is a plan view of a piezoelectric element;

FIG. 10H is a sectional view taken along the direction indicated byarrows Z in FIG. 10G illustrating the element;

FIG. 10I is a plan view of a piezoelectric element;

FIG. 10J is a sectional view taken along the direction indicated byarrows Z in FIG. 10I illustrating the element;

FIG. 10K is a plan view of a piezoelectric element;

FIG. 10L is a sectional view taken along the direction indicated byarrows Z in FIG. 10K illustrating the element;

FIG. 11 is a perspective view of a unimorph piezoelectric element;

FIG. 12 is a longitudinal sectional view taken along the directionindicated by an arrow Z in FIG. 11 illustrating the piezoelectricelement;

FIG. 13 is a perspective view of a unimorph piezoelectric element;

FIG. 14 is a longitudinal sectional view taken along the directionindicated by an arrow Z in FIG. 13 illustrating the piezoelectricelement;

FIG. 15 is a perspective view of a bimorph piezoelectric element;

FIG. 16 is a longitudinal sectional view taken along the directionindicated by an arrow Z in FIG. 15 illustrating the piezoelectricelement;

FIGS. 17A top 17C are views for explaining the operation of thepiezoelectric element in FIG. 15;

FIG. 17D is a sectional view showing the piezoelectric element fixed toa substrate via support members;

FIG. 18A is a plan view of a piezoelectric element;

FIG. 18B is a sectional view taken along the direction indicated byarrows Z in FIG. 18A illustrating the element;

FIG. 19A is a plan view of a piezoelectric element;

FIG. 19B is a sectional view taken along the direction indicated byarrows Z in FIG. 19A illustrating the element;

FIG. 20A is a plan view of a piezoelectric element;

FIG. 20B is a sectional view taken along the direction indicated byarrows Z in FIG. 20A illustrating the element;

FIG. 21A is a plan view of a piezoelectric element;

FIG. 21B is a sectional view taken along the direction indicated byarrows Z in FIG. 21A illustrating the element;

FIG. 22A is a plan view of a piezoelectric element;

FIG. 22B is a sectional view taken along the direction indicated byarrows Z in FIG. 22A illustrating the element;

FIG. 23A is a plan view of a piezoelectric element;

FIG. 23B is a sectional view taken along the direction indicated byarrows Z in FIG. 23A illustrating the element;

FIG. 24 is a perspective view of a piezoelectric element;

FIG. 25 is a longitudinal sectional view taken along the directionindicated by an arrow Z in FIG. 24 illustrating the piezoelectricelement;

FIG. 26 is a perspective view of a bimorph piezoelectric element;

FIG. 27 is a sectional view taken along the direction indicated by anarrow Z in FIG. 26 illustrating the element;

FIG. 28 is a perspective view of a bimorph piezoelectric element;

FIG. 29 is a sectional view taken along the direction indicated by anarrow Z in FIG. 28 illustrating the element;

FIG. 30 is a perspective view of a bimorph piezoelectric element;

FIG. 31 is a perspective view of a bimorph piezoelectric element;

FIG. 32 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter in accordance with another embodiment;

FIG. 33 is a perspective view of a vibrator;

FIG. 34 is a front view of the vibrator shown in FIG. 33;

FIG. 35 is a waveform chart showing waveforms at respective sections inthe circuit shown in FIG. 32;

FIG. 36 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter in accordance with another embodiment;

FIG. 37 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter in accordance with another embodiment;

FIG. 38 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter in accordance with another embodiment;

FIG. 39 is a perspective view of a vibrator;

FIG. 40 is a front view of the vibrator shown in FIG. 39;

FIG. 41 is a perspective view of a vibrator;

FIG. 42 is a front view of the vibrator shown in FIG. 41;

FIG. 43 is a perspective view of a vibrator;

FIG. 44 is a front view of the vibrator shown in FIG. 43;

FIG. 45 is a perspective view of a vibrator;

FIG. 46 is a front view of the vibrator shown in FIG. 45;

FIG. 47 is a perspective view of a vibrator;

FIG. 48 is a front view of the vibrator shown in FIG. 47;

FIG. 49 is a perspective view of a vibrator;

FIG. 50 is a front view of the vibrator shown in FIG. 49;

FIG. 51 is a perspective view of a vibrator;

FIG. 52 is a front view of the vibrator shown in FIG. 51;

FIG. 53 is a perspective view of a vibrator;

FIG. 54 is a front view of the vibrator shown in FIG. 53;

FIG. 55 is a view showing a comparative self-excitation circuit;

FIG. 56 is a circuit diagram of a piezoelectric vibrational angularvelocity meter;

FIG. 57 is a timing chart showing an operation of an excitation drivingcircuit;

FIG. 58 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter;

FIG. 59 is a timing chart showing an operation of an excitation drivingcircuit;

FIG. 60 is a circuit diagram of a piezoelectric vibrational angularvelocity meter;

FIG. 61 is a circuit diagram of a piezoelectric vibrational angularvelocity meter;

FIG. 62 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter;

FIG. 63 is a timing chart showing an operation of an excitation drivingcircuit;

FIG. 64 is a circuit diagram showing a comparative piezoelectricvibrational angular velocity meter;

FIG. 65 shows output waveforms of the self-excitation driving circuit inthe piezoelectric vibrational angular velocity meter shown in FIG. 64;and

FIG. 66 is a block diagram showing a camera system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a piezoelectric element according to an embodiment ofthe present invention.

A piezoelectric element PED1 comprises first and second piezoelectricelements. The first piezoelectric includes a first member 1, anelectrode 6, and electrodes 3, 4, and 5. The electrode 6 and theelectrodes 3, 4, and 5 sandwich the first member 1. The secondpiezoelectric element includes a second member 2 and electrodes 8 and 9which sandwich the second member 2.

Each of the first and second members 1 and 2 is made of a piezoelectriccrystal such as PZT. Each of the electrodes 3, 4, 5, 6, 8, and 9 is madeof a silver paste. The lower surface of the first piezoelectric elementis fixed to the upper surface of the second piezoelectric element via anadhesive layer 7.

A direction perpendicular to both the longitudinal direction and thedirection of thickness of the first member 1 is defined as a “lateraldirection” or “widthwise direction”. The middle electrode 3 of the firstpiezoelectric element is arranged between the right and left electrodes5 and 4. There are gaps between the middle electrode 3 and the rightelectrode 5 and between the middle electrode 3 and the left electrode 4.These electrodes 3, 4, and 5 are electrically insulated from each other.The electrodes 3, 4, and 5 extend parallel in the longitudinaldirection.

The adhesive layer 7 between the lower surface of the lower-surfaceelectrode 6 of the first piezoelectric element and the upper-surfaceelectrode 8 of the second optical axis element is electricallyinsulated. Both the lower surface of the lower-surface electrode 6 ofthe first piezoelectric element and the upper surface of theupper-surface electrode 7 of the second piezoelectric element are rough.The adhesive layer 7 has a thickness of 1 mm or less. For these reasons,these electrodes 6 and 7 are electrically connected to each other.

The piezoelectric element PED1 is supported by ring-like support membersB1 and B2. The rubber rings B1 and B2 are wound on the piezoelectricelement PED1. Each of the rings B1 and B2 is made of silicone rubber andis fixed to a substrate 12 via adhesive layers 10 and 11. A node setwhen the piezoelectric element PED1 vibrates in a nonrestraint state isa point that remains still when the piezoelectric element PED1 vibrateswithout being supported anywhere. Two nodes are set. The piezoelectricelement PED1 is supported by the support members B1 and B2 at thepositions of these two nodes to be fixed to the substrate 12. Thesupport members B1 and B2 respectively have support portions B1a andB2a.

The substrate 12 is a glass plate. The substrate 12 may be made ofalumina.

One edge of the piezoelectric element PED1 is slightly cut. That is, aportion of the electrode 4 is cut, and the edge defined by the upper andside surfaces of the first piezoelectric element is smoothly arcuated.The first member 1 has an arcuated edge surface 13. When a portion ofthe piezoelectric element PED1 is cut, its natural oscillation frequencychanges. A portion of the piezoelectric element PED1 is cut to adjustits natural oscillation frequency so as to match the frequency of an ACvoltage to be applied between the electrodes 8 and 9.

Lead lines (wires) 3a, 4a, 5a, 6a, and 9a are electrically connected tothe electrodes 3, 4, 5, 6, and 9, respectively.

The first and second members 1 and 2 have undergone polarization. Thepolarizing direction coincides with the direction of thickness of themembers 1 and 2.

FIG. 3A shows the piezoelectric element in FIG. 1, a circuit unit fordriving the piezoelectric element, and a case for housing them.

The glass plate 12 is fixed to a circuit board 14a via an adhesive layer14. A circuit unit 15 is mounted on the lower surface of the circuitboard 14a. The lead lines 3a, 4a, 5a, 6a, and 9a are electricallyconnected to the circuit unit 15 via terminals 143a, 144a, 145a, 146a,and 149a arranged on the upper surface of the circuit board 14a.

Four holes 18a to 21a are formed in the corner portions of the circuitboard 14a. Screws 18 to 21 extend through these holes 18a to 21a,respectively. These screws 18 to 21 are threadably engaged with screwholes 18b to 21b formed in the upper surface of a lower case 16. Thecircuit board 14a is, therefore, fixed to the lower case 16. The lowercase 16 is made of a plastic material.

A large cavity capable of housing the circuit unit 15 is formed in thecenter of the lower case 16. When the circuit board 14a is fixed to thelower case 16, the circuit unit 15 is housed in this cavity.

An input pin 18c, an output pin 19c, and a GND pin 21c extend downwardfrom the circuit board 14a. These terminals 18c, 19c, and 21c areconnected to the circuit unit 15. An input voltage is applied from theoutside of the element in FIG. 3A to the circuit unit 15 via the inputpin 18c. The GND pin 21c is connected to the earth (ground). An outputvoltage is output from the circuit unit 15 to the outside of thiselement via the output pin 19c.

FIG. 3B shows a piezoelectric angular velocity meter. This element isobtained by mounting a cover (upper case) 22 on the upper surface of theelement in FIG. 3A. The cover 22 is made of a metal. There is anadhesive (seal agent) layer 23 between the outer surface of the openingedge portion of the cover 22 and the inner surface of the opening edgeportion of the lower housing. The airtightness in the case is maintainedby the adhesive layer 23.

FIG. 4A shows a camera using a piezoelectric angular velocity meter(sensor) YJ1 in FIG. 3B.

This camera also includes a sensor JY2. The sensor JY2 has the samestructure as that of the sensor JY1. The sensors JY1 and JY2 arearranged within the X-Y plane. The longitudinal directions ofpiezoelectric elements PED1 arranged in these sensors JY1 and JY2 areperpendicular to each other.

The optical axis of a lens of the camera is defined as the Z-axis. TheX-axis, the Y-axis, and Z-axis in FIG. 4A are perpendicular to eachother. This camera has a housing 410, in which the sensors JY1 and JY2are arranged. The rotational angular velocity (pitching amount) of thecamera which rotates about the X-axis is detected by the sensor JY1. Therotational angular velocity (pitching amount) of the camera whichrotates about the Y-axis is detected by the sensor JY2.

This camera includes lenses 403, 404, 405, and 406. Image light passingthrough these lenses is focused on a film 411 arranged in the housing410. The lens 404 is moved in the X direction by a coreless motor 401,and is moved in the Y direction by a coreless motor 402.

While this camera is not rotated, an optical axis OA1 of the lens 404extends through a center A′ of the film 411. Light from an object A,therefore, passes through the center A′ of the film 411 (see FIG. 4B).

Let R (cm) be the distance from the X-Y plane (film surface) to the lens404, and Ω (rad/sec) be the angular velocity detected by the sensor JY1.When the lens 404 is fixed to the housing 410 so as not to move, thelens 404 rotates about the X-axis at the angular velocity Ω (rad/sec),together with the camera (see FIG. 4C). At this time, the lens 404 ismoved in the −Y direction at about a velocity R×Ω(cm/sec), together withthe camera.

In this case, the focal point of light from the object A shifts from thepoint A′ to a point A″ on the film 411.

The camera of this embodiment includes a central processing unit 502.The central processing unit 502 controls the motor 401 to move the lens404 in accordance with the angular velocity detected by the sensor JY1.When the angular velocity detected by the sensor JY1 is Ω (rad/sec), thelens 404 is moved in the +Y direction with respect to the housing 410 atabout the velocity R×Ω (cm/sec) (see FIG. 4D). Even if, therefore, thecamera rotates about the X-axis, an image of the object A does not movewith respect to the film 411.

Similarly, when the lens 404 is fixed to the housing 410 so as not tomove, and the camera rotates about the Y-axis at the angular velocity Ω(rad/sec), the lens 404 is moved in −X direction at about the velocityR×Ω (cm/sec).

The central processing unit 502 controls the motor 402 to move the lens404 in accordance with the angular velocity detected by the sensor JY2.When the angular velocity detected by the sensor JY2 is Ω (rad/sec), thelens 404 is moved in the +X direction with respect to the housing 410 atabout the velocity R×Ω (cm/sec) (see FIG. 4D). Even if, therefore, thecamera rotates about the Y-axis, an image of the object A does not movewith respect to the film 411.

Note that this camera, similar to a general camera, includes a releasebutton (shutter button) 407, a liquid crystal display 408 for displayingan exposure value and the frame count of the film, and a finder 409.

The circuit unit 15 shown in FIG. 3B will be described next.

FIG. 5 is a block diagram showing the piezoelectric element in FIG. 1and a circuit connected thereto. FIGS. 6A and 6B are timing charts forexplaining the operation of the circuit in FIG. 5. Voltage waveforms Ato J, R1, R2, L1, L2, and DO respectively correspond to the voltagewaveforms at points A to J, R1, R2, L1, L2, and DO in FIG. 5. Inaddition, voltage waveforms A′, A″, B′, C′, D′, F′, and G′ in FIGS. 6Aand 6B respectively correspond to the voltage waveforms at points A, B,C, D, F, and G in FIG. 5.

An antivibration circuit for the piezoelectric element will be describedfirst.

The second piezoelectric element is used to vibrate the firstpiezoelectric element. A triangular wave “A” generating circuit 550applies a triangular wave voltage between the lower-surface electrode 9of the second piezoelectric element and the ground electrode 6 (see FIG.6A (a)). The frequency of the triangular wave is about 39 MHz. Thefrequency of the triangular wave matches the natural oscillationfrequency of the piezoelectric element PED1.

When an AC voltage matching the natural oscillation frequency of thepiezoelectric element PED1 is applied from the triangular wavegenerating circuit 550 to the second piezoelectric element, the secondpiezoelectric element vibrates. Since the first piezoelectric element isfixed to the second piezoelectric element, the first piezoelectricelement also vibrates. When the first piezoelectric element vibrates, ACvoltages are respectively induced between the ground electrode 6 and thethree electrodes 3, 4, and 5 of the first piezoelectric element owing tothe piezoelectric effect.

The middle electrode 3 of the first piezoelectric element is used tokeep vibration constant. The voltage waveform between the middleelectrode 3 and ground is indicated by “B” in FIG. 6A (b).

A preamplifier 551 is connected to the middle electrode 3. Thepreamplifier 551 inverts the phase of an input voltage signal andoutputs the resultant signal. The waveform of the voltage output fromthe preamplifier 551 is indicated by “C” in FIG. 6A (c).

First and second comparators 552 and 553 are connected to thepreamplifier 551.

The first comparator 552 receives both a signal from the preamplifier551 and a signal from a first reference voltage generating circuit 552a.The level of the first reference voltage is represented by V₁ref. If avoltage signal output from the preamplifier 551 is higher than the levelV₁ref, the first comparator 552 outputs a low-level voltage signal. If avoltage signal output from the preamplifier 551 is lower than the levelV₁ref, the first comparator 552 outputs a high-level voltage signal. Thewaveform output of the voltage from the first comparator 552 isindicated by “D” in FIG. 6A (d).

An integrating circuit (level monitor) 554 is connected to the firstcomparator 552. The integrating circuit 554 integrates an input signaland outputs the resultant signal. A voltage signal output from the firstcomparator 552 is integrated by the integrating circuit 554, which thanoutputs a DC voltage F in FIG. 6A (d).

The second comparator 553 receives both a signal from the preamplifier551 and a signal from a second reference voltage generating circuit553a. The level of the second reference voltage is represented by V₂ref.If a voltage signal output from the preamplifier 551 is higher than thelevel V₂ref, the second comparator 553 outputs a low-level voltagesignal. If a voltage signal output from the preamplifier 551 is lowerthan the level V₂ref, the second comparator 553 outputs a high-levelvoltage signal. The level V₂ref is lower than the level V₁ref. The levelV₂ref crosses the operating point of an input AC voltage. The waveformof the voltage output from the second comparator 553 is indicated by “E”in FIG. 6A (e).

Both a voltage signal output from the second comparator 553 and avoltage signal output from the integrating circuit 554 are input to amultiplier (switch) 555. The multiplier 555 multiplies the outputvoltage from the second comparator 553 and the output voltage from theintegrating circuit 554, and outputs the product. The multiplier 555switches the output voltage from the integrating circuit 554 insynchronism with the output voltage from the second comparator 553. Theoutput from the second comparator 553 is a square wave voltage, and theoutput from the integrating circuit 554 is a DC voltage. For thisreason, the output from the multiplier 555 is a square wave voltage. Thewaveform of the voltage output from the multiplier 555 is indicated by“G” in FIG. 6A (f).

The triangular wave generating circuit 550 integrates the square wavevoltage output from the multiplier 555, and outputs the resultantvoltage. The voltage B detected by the middle electrode 3 delays inphase with respect to the voltage A′ output from the triangular wavegenerating circuit 550 by 90°.

Since the piezoelectric element PED1 detects a strain corresponding toan angular velocity as a voltage, the amplitude of vibration may change.Assume that the amplitude of an AC voltage induced by the firstpiezoelectric element increases, as indicated by “B” and “B′” in FIG. 6A(b). In this case, the amplitude of the output voltage from thepreamplifier 551 also increases, as indicated by “C′”. Therefore, thetime during which the voltage is higher than the level V₁ref isprolonged, and the pulse width of the square wave output from the firstcomparator 552 increases as indicated by “D′”. As a result, the level ofthe DC voltage output from the integrating circuit 554 decreases. Theamplitude of the square wave output from the multiplier 555 alsodecreases. Consequently, the amplitude of the triangular wave outputfrom the triangular wave generating circuit 550 decreases.

As described above, if the amplitude of an AC voltage induced by thefirst piezoelectric element increases as indicated by “B′”, thisautomatic level control circuit controls the triangular wave generatingcircuit 550 to decrease this amplitude. If the amplitude of the ACvoltage induced by the first piezoelectric element decreases, theautomatic level control circuit controls the triangular wave generatingcircuit 550 to increase this amplitude. The automatic level controlcircuit comprises the comparators 552 and 553, the integrating circuit554, the multiplier 555, and the reference voltage generating circuits552a and 553a.

A rotational angular velocity detection circuit will be described next.

Assume that while the piezoelectric element PED1 is vibrating along theZ-axis direction, the piezoelectric element PED1 rotates about theX-axis. In this case, a Coriolis force acts on the piezoelectric elementPED1 in the Y-axis direction, and the piezoelectric element PED1deflects in the Y-axis direction (lateral direction). At this time, anAC voltage L1 induced between the left electrode 4 and the groundelectrode 6 is different in amplitude from an AC voltage R1 inducedbetween the right electrode 5 and the ground electrode 6 (see FIG. 6B).Note that the waveform B in FIG. 6B (a) indicates the waveform of thevoltage output from the left and right electrodes 4 and 5 when noCoriolis force acts on the piezoelectric element.

A preamplifier 556 is connected to the left electrode 4 of the firstpiezoelectric element. A preamplifier 557 is connected to the rightelectrode 5. The preamplifiers 556 and 557 invert the phases of inputvoltage signals and amplify them. The amplification factor is, forexample, 2.2. The waveform of the voltage output from the preamplifier556 indicated by “L2” in FIG. 6B (b). The waveform of the voltage outputfrom the preamplifier 557 is indicated by “R2” in FIG. 6B (b).

The signals L2 and R2 output from the preamplifiers 556 and 557 areinput to a differential amplifier 558. As shown in FIG. 6B (c), avoltage signal DO representing the difference between the voltagesignals L2 and R2 is output from the differential amplifier 558. Thisdifference signal DO corresponds to the Coriolis force acting on thepiezoelectric element PED1, i.e., the rotational angular velocity of thepiezoelectric element.

The signal output from the differential amplifier 558 is input to amultiplier 559. The multiplier 559 multiplies the voltage signal DOoutput from the multiplier 555 and a signal H output from thedifferential amplifier 558 and passing through a phase shifter 562, andoutputs the resultant signal. The phase shifter 562 adjusts the phase ofa signal G output from the multiplier 555 such that the differentialoutput DO is synchronous with the output G.

As shown in FIG. 6B (d), a voltage signal I output from the multiplier559 passes through a low-pass filter 560. A DC component J of the signalis output from the low-pass filter 560. The level of the DC voltage Jcorresponds to the Coriolis force acting on the piezoelectric elementPED1, i.e., the rotational angular velocity of the piezoelectricelement.

The DC voltage J is amplified by a gain adjustment amplifier 561 and isoutput from the output terminal 19c.

As described above, a signal corresponding to the angular velocity ofrotation about the X-axis is output from the piezoelectric angularvelocity meter JY1. The piezoelectric angular velocity meter JY2 has thesame structure as that of the meter JY1. A signal corresponding to theangular velocity of rotation about the Y-axis is output from the angularvelocity meter JY2.

FIG. 7 shows a camera system for moving a lens on the basis of signalsoutput from the piezoelectric angular velocity meters.

The signals output from the angular velocity meters JY1 and JY2 areconverted into digital signals by an A/D converter 501. Data output fromthe A/D converter 501 are input to the central processing unit (CPU)502. The motors 401 and 402 are driven by a driving circuit 503. Thecentral processing unit 502 controls the driving circuit 503 to rotatethe motor 401. The method of controlling the lens 404 through thecentral processing unit 502 has been described with reference to FIGS.4A to 4D.

Each piezoelectric angular velocity meter will be described in detailbelow.

When the above vibrator PED1 causes natural oscillation and rotatesabout the vibrator axis, a Coriolis force FC is generated in a directionperpendicular to the two directions. This force FC is given by:Fc=2m (V·Ω)  (1)where m is the mass of the vibrator, v is the vibration speed of thevibrator, and Ω is the rotational angular velocity.

In a conventional vibration angular velocity meter, problems are posedin manufacturing inexpensive, compact vibrators. More specifically, whenthe manufacturing process includes the process of joining piezoelectricceramic plates to metal vibrators, piezoelectric ceramic plates must bejoined to vibrator side surfaces one by one. This process needs muchtime, posing difficulty in realizing mass production. In the process,the workability deteriorates as the size of each vibrator decreases.When electrodes are to be formed on the side surface of cylindricalpiezoelectric ceramic member, the electrodes must be formed on vibratorsone by one by using a roll type printing machine. In addition, eachvibrator must be polarized. Such a process is not suitable for massproduction and a reduction in size either.

If electrodes are two-dimensionally formed on a ceramic plate consistingof a piezoelectric or electrostrictive material, compact vibrators canbe manufactured in large quantities at once. In consideration of such atechnique, there is provided a piezoelectric vibration angular velocitymeter having a unimorph structure including a metal or ceramic basemember in the form of a quadratic prism, a vibrator constituted by apiezoelectric or electrostrictive member in the form of a quadraticprism, an inner electrode formed between the base member and thepiezoelectric or electrostrictive member, and an outer electrode formedon the side surface of the piezoelectric or electrostrictive memberwhich is located on the opposite side to the inner electrode.

Note that the ceramic material includes a glass material, a sinteredpolycrystalline material, a synthetic single crystal, and the like.

Unimorph vibrators can be manufactured in large quantities by joining apiezoelectric or electrostrictive ceramic or plate having electrodepatterns formed on both the surfaces to a metal or ceramic plate havingthe same size as that thereof, and cutting the resultant structure. Inaddition, if the electrode patterns are formed by lithography, and thejoint plate is cut with a precision cutter, compact unimorph vibratorscan be manufactured with good reproducibility.

Nonrestraint fundamental vibration of a unimorph vibrator is excited byusing a so-called piezoelectric lateral effect by applying a voltagebetween an inner electrode as a ground electrode on a piezoelectric orelectrostrictive member and the middle electrode of three divided outerelectrodes. The vibration, therefore, is caused in a directionperpendicular to the electrode surface. When the vibrator rotates aboutthe axis of the vibrator, the vibrator is bent within the electrodesurface owing to the Coriolis force. This bending due to the Coriolisforce is detected by the two detection electrodes of the three dividedouter electrodes which are located on both sides.

At this time, since piezoelectric signals are generated in the Coriolisforce detection electrodes upon driving of the vibrator, actual signalsare signals obtained by synthesizing signals originating from theCoriolis force and signals originating from the driving of the vibrator.The signals generated in the two detection electrodes have the samefrequency, are opposite in phase with respect to the Coriolis force, andare in phase with respect to the driving operation. If, therefore,differential voltages between the signals are obtained, only signalsalmost originating from the Coriolis force can be obtained.

FIGS. 8A and 8B show a vibration angular velocity meter PED2 of thesecond embodiment. A rectangular parallellepiped member 81 consists of apiezoelectric material. Electrodes 83, 84, 85, and 86 formed on the twoopposite surfaces of the upper member 81. The upper member is joined toa lower rectangular parallellepiped member 82 consisting of a silicaglass material with an adhesive layer 87 such that the electrode 86serving as an inner electrodes becomes a joint surface. The electrodes83, 84, and 85 on the piezoelectric member 81, i.e., the upper surfaceof the vibrator, are isolated from each other to be symmetrical aboutthe central axis of the vibrator. The middle electrode 83 is used for adriving operation, and the electrodes 84 and 85 on both sides are usedfor detection. The inner electrode 86 serving as a ground electrode isformed on the entire surface without being divided. The piezoelectricmember 81 is polarized in the direction of thickness. A cross-section ofthe vibrator which is perpendicular to the direction of a vibrator axisΩ is almost square to match the resonance frequency in the direction ofa velocity V of the direction of thickness with the resonance frequencyin the direction of the Coriolis force Fc.

FIGS. 9A to 9C show the operation principle of the piezoelectricvibration angular velocity meter in FIG. 8A. The vibrator in FIG. 8Avibrates under a nonrestraint condition, and the central portion betweennodes N1 and N2 of the vibration and the end portions have velocities inopposite directions (see FIG. 9A). When the vibrator rotates about thevibrator axis C1, Coriolis forces Fc are exerted on a central portion Ω,between the nodes N1 and N2 of the vibration and end portions E1 and E2in the opposite directions (see FIG. 9B). With these forces Fc, thevibrator is bent in a direction within the electrode surface (within aplane perpendicular to the direction of thickness) (see FIG. 9C). In thetwo detection electrodes 84 and 85 on both sides, piezoelectric signalsoriginating from the driving/vibration shown in FIG. 19A andpiezoelectric signals originating from the deformation due to theCoriolis forces in FIG. 9C are generated at the same time. Of thesesignals, the piezoelectric signals originating from the Coriolis forcesare almost opposite in phase between the two electrodes 84 and 85. Thisis because in, for example, the deformed state in FIG. 9C, a compressionstress acts on the electrode 84 side and, and a tensile stress acts onthe electrode 85 side. That is, stresses acting on the two electrodes 84and 85 always have opposite signs. In contrast to this, thepiezoelectric signals originating from the driving operation andgenerated in the two electrodes 84 and 85 are almost identical. If,therefore, differential signals between the piezoelectric signals in thetwo electrodes 84 and 85 are obtained, only the piezoelectric signalsalmost originating from the Coriolis force can be obtained. Since thevibrator has a square cross-section to match the resonance frequency inthe Coriolis force direction with the resonance frequency in the drivingdirection, if outputs from the detection electrodes 84 and 85 are fedback, the vibrator can be driven at a frequency near the resonancefrequency by a simple oscillation circuit. Therefore, the vibrationbased on the Coriolis force is also set in a resonant state to improvethe detection sensitivity.

The vibrator, however, need not be designed such that the resonance inthe driving direction matches the resonance frequency in the Coriolisforce direction. For example, even if a resonant state is not set in adriving operation, unimorph vibration with a large displacement can beused, and resonance in the Coriolis force direction can be used only fordetection. For this purpose, the vibrator my be subjected to unimorphdriving at the resonance frequency in the Coriolis force direction. Withsuch a vibrator, the resonance matching step can be omitted.

FIG. 9D shows a method of supporting the vibrator to realize thenonrestraint vibration condition of the vibrator in FIG. 8A. Supportportions 89a and 89b are fixed to the plate 82 at positionscorresponding to the nodes N1 and N2 of vibration with an adhesive, andthe support portions 89a and 89b are fixed to a support base 88 with asilicone-based adhesive. The overall vibrator may be simply embedded inan adhesive having a relatively low elastic constant.

FIGS. 10A to 10L show a manufacturing process for the piezoelectricvibration angular velocity meter in FIG. 8A. A plate 25 made of apiezoelectric material polarized in the direction of thickness andhaving silver electrodes 24 and 26 on the upper and lower surfaces isjoined to a silica glass plate 27 having a shape similar to the plate 25with an epoxy-based adhesive layer 28 (see FIGS. 10A and 10B). In orderto maintain high positioning precision in the subsequent steps, theperipheral portion of the joint plate is cut with a dicing saw to alignthe side surfaces of the two plates (FIGS. 10C and 10D). A photoresistfilm 29 is formed on the surface of one electrode 24, and a resistpattern corresponding to an electrode pattern having electrodes of thesame width at equal intervals is formed by an exposure apparatus (FIGS.10E and 10F). The exposed portions of the silver electrode 24 areremoved by reactive ion etching using this resist 29 as a protectivemask (FIGS. 10G and 10H). Thereafter, the resist 29 is removed (FIGS.10G and 10J), and every other electrode of the remaining bar-likeelectrodes 24 is cut at its middle portion, thereby manufacturing avibrator having a driving electrode 83 formed in the middle anddetection electrodes formed on both sides thereof, which electrodes aresymmetrical about the central axis of the vibrator (FIGS. 10K and 10L).According to this process, a large number of compact unimorphpiezoelectric vibration angular velocity meters can be manufactured fromone joint structure of a piezoelectric plate and a silica glass plate.

An inexpensive, compact piezoelectric vibration angular velocity metersimilar to the one described above can be manufactured by using a metalplate as a member constituting a unimorph structure instead of a ceramicmaterial such as silica glass. In this case, the metal member can beused as parts of electrodes and leads.

As described above, according to the present invention, inexpensive,compact vibration angular velocity meters can be provided in largequantities.

FIGS. 11 and 12 show a piezoelectric vibration angular velocity meteraccording to the third embodiment. A unimorph structure as a vibrator ismanufactured by joining a piezoelectric member 101 to a metal member 102whose thermal expansion coefficient is matched with that of thepiezoelectric member 101. Two divided outer electrodes 104 and 105 areformed on a surface of the piezoelectric member 101, and an innerelectrode 106 is formed entirely on the opposite surface of the innerelectrode 106 to the surface on which the electrodes 104 and 105 areformed. The piezoelectric member 101 is polarized in a directionperpendicular to the electrode surface. The vibrator is joined on ametal plate 109. The metal plate 109 is joined to a plate 110constituted by a piezoelectric member 110a having electrodes 110b and110c formed on both surfaces. This plate 110 is fixed to a support base111. The shape of the vibrator is designed such that the resonancefrequencies of an element DEP3 in a normal direction (indicated by “V”in FIG. 11) with respect to the electrode surface become almost thesame. Leads 104a and 105a extend from the divided electrodes 104 and 105on the fixed end portion of the vibrator PED3 to connect the metalmember 102 and the metal plate 109 of the vibrator to ground.

An AC voltage having a frequency near the resonance frequency of thefundamental cantilever natural oscillation of the uniform vibrator PED3is applied to the piezoelectric plate 110 to cause resonant vibration ofthe vibrator. When the vibration is caused in the direction (indicatedby “V” in FIG. 11) perpendicular to the electrode surface to causerotation (indicated by “Ω” in FIG. 11) about the axis of the vibrator,the vibrator is bent within the electrode surface owing to the Coriolisforce (“Fc” in FIG. 11). Owing to this force, a compression stress isgenerated on the right side (electrode 105 side) of the vibrator and atensile force is generated on the left side (electrode 104 side) of thevibrator with respect to the central axis of the vibrator. At this time,piezoelectric signals originating from the Coriolis force, which areobtained from the two divided detection electrodes 104 and 105 becauseof the piezoelectric lateral effect, have opposite phases. In contrastto this, piezoelectric signals originating from the stresses upondriving of the vibrator and generated in the two divided electrodes arein phase. In general, since a signal generated by a driving operation islarger than a signal generated by a Coriolis force, it is difficult toread the Coriolis force from a signal obtained by synthesizing the twosignals. For this reason, the difference between the signals obtainedfrom the two divided electrodes is obtained, and the gain and phase areadjusted, thereby canceling out the piezoelectric signals generated bythe driving operation. With this operation, only the signals generatedby the Coriolis force can be extracted. Note that the respective membersare fixed with adhesive layers 107, 108, 112, and 113. Lead lines 1110band 1110c are respectively connected to the electrodes 110b and 110c.

FIGS. 13 and 14 show a piezoelectric vibration angular velocity meterPED4 according to the fourth embodiment. Electrodes 203, 204, 205, and206 are formed on the opposite surfaces of a piezoelectric member 201constituting the vibrator. The three divided electrodes 203, 204, and205 serving as outer electrodes are formed with reference to the centralaxis of the vibrator, and the inner electrode 206 is formed on theentire surface. Polarization is performed in a direction perpendicularto the electrode surface. This piezoelectric member 201 is joined topart of the vibrator made of a free-machining ceramic material and aprop 202 via the inner electrode 206 with an adhesive 214. The prop 202is also embedded/fixed in/to a support base 212 made of a ceramicmaterial with an adhesive layer 213. Leads 203a, 204a, and 205arespectively extend from the divided electrodes 203, 204, and 205 on thefixed end portion of the vibrator, and a lead 206a also extends from theinner electrode 206. The shape of the vibrator is designed such that theresonance frequency in the normal direction (indicated by “V” in FIG.13) with respect to the electrode surface is almost equal to that in theCoriolis force direction (indicated by “F” in FIG. 13). The outerelectrode 203 in the middle is used for a driving operation. When an ACvoltage having a frequency near the resonance frequency of thefundamental natural oscillation of the unimorph vibrator is applied,resonant vibration in the normal direction (indicated by “V” in FIG. 13)with respect to the electrode surface is caused. At this time, when thevibrator rotates about the axis of the vibrator, the vibrator is bentwithin the electrode surface owing to the Coriolis force (“Fc” in FIG.13). By obtaining the difference between piezoelectric signals generatedin the two electrodes on both the sides of the middle electrode bystresses caused upon this bending, the Coriolis force can be detected bythe same method as that described in the third embodiment.

If the vibrator is caused to vibrate under cantilever vibrationconditions with one end of the vibrator being fixed, and the other endbeing set in a nonrestraint state, the vibrator can be easily fixed, andlead lines can be joined to electrode portions on the fixed portionwhich does not vibrate. Therefore, an almost ideal vibration state canbe obtained. This device has a unimorph structure including arectangular parallellepiped base member consisting of a metal or ceramicmaterial, a vibrator constituted by a parallellepiped piezoelectric orelectrostrictive member joined to the base member, an inner electrodeformed between the base member and the piezoelectric or electrostrictivemember, and outer electrodes on the opposite side surface of thepiezoelectric or electrostrictive member to the inner electrode. One endof the vibrator is fixed.

Cantilever vibration allows the vibrator to be easily fixed, and alsoallows lead lines to be connected to the fixed portion which does notvibrate so that an ideal vibration state can be easily attained. Thevibrator is preferably shaped into a quadratic prism, which allows easyformation of a unimorph structure and easy adjustment of the resonancefrequency.

By vibrating the piezoelectric or electrostrictive element as anexcitation means, fundamental cantilever vibration of the unimorphvibrator can be excited. Vibration is caused in a directionperpendicular to the electrode surface. When the vibrator rotates aboutthe axis of the vibrator, the vibrator is bent within the electrodesurface owing to the Coriolis force. Of the signals generated in the twodivided outer electrodes, the signals originating from the Coriolisforce have opposite phases between the two electrodes, and the signalsoriginating from the driving operation are in phase. If, therefore, thedifferential signal between the two signals is obtained, only thesignals almost originating from the Coriolis force can be obtained.

If three divided outer electrodes are formed on a piezoelectric orelectrostrictive member constituting a unimorph structure, the middleelectrode is used for excitation to excite fundamental cantilevernatural oscillation. If the electrodes on both sides are used fordetection, and the differential voltage between the two signalsgenerated in the two electrodes is obtained, signals originating fromthe Coriolis force can be obtained.

According to the above method, a vibration angular velocity meter havingan ideal vibration condition can be easily provided. In addition,inexpensive, compact vibrators can be manufactured in large quantitiesby forming an electrode pattern on a large ceramic plate by printing,photolithography, or the like, joining a metal or ceramic plate to theceramic plate, and cutting the resultant structure.

FIGS. 15 and 16 show a vibration angular velocity meter PED5 accordingto the fifth embodiment. Rectangular parallellepiped members 301 and 302consisting of a piezoelectric material and having electrodes 304, 305,306, 308, and 310 on the two opposite surfaces of each member are joinedto each other by joining the electrode surfaces to each other. Thepiezoelectric member 301 serving as a detection member has theelectrodes 304 and 305 isolated from each other on the upper surface ofthe vibrator to be symmetrical about the central axis of the vibrator.The piezoelectric member 302 serving as a detection member has both theelectrodes 306 and 310 respectively formed on the entire surfaces. Boththe piezoelectric members are polarized in a direction perpendicular tothe electrodes. A cross-section of the vibrator in a directionperpendicular to the axis of the vibrator has almost a square shape tomatch the resonance frequency in the driving direction with theresonance frequency in the Coriolis force direction.

FIGS. 17A to 17C show the operation principle of the vibration angularvelocity meter PED5 in FIG. 16. The vibrator vibrates under anonrestraint condition, and a central portion C1 and end portions E1 andE2 of the vibrator have velocities in opposite directions with respectto nodes N1 and N2 of vibrator as boundaries (FIG. 17A). At this time,when the vibrator rotates about an axis Ω of the vibrator, since thecentral portion C1 and the end portions E1 and E2 have velocities in theopposite directions, Coriolis forces are generated in the oppositedirections with respect to the nodes N1 and N2 of vibration asboundaries (FIG. 17B). Owing to these Coriolis forces, the vibrator isbent in a direction within the electrode surface (FIG. 17C). In the twodivided detection electrodes 304 and 305, piezoelectric signals (FIG.17C) originating from the driving operation (FIG. 17A), andpiezoelectric signals originating from deformation caused by theCoriolis forces are generated at the same time. Of these signals, thepiezoelectric signals originating from the Coriolis forces and generatedin the two electrodes 304 and 305 have almost opposite phases. This isbecause, in the deformation state shown in FIG. 17C, for example, acompression stress acts on the electrode 304 side, and a tensile stressacts on the electrode 305 side, and stresses acting on the twoelectrodes always have opposite signs. In contrast to this, thepiezoelectric signals originating from the driving operation andgenerated in the two electrodes 304 and 305 are almost in phase.Therefore, only the piezoelectric signals almost originating from theCoriolis forces can be obtained by obtaining differential signals fromthe two electrodes 304 and 305.

FIG. 17D shows a vibrator supporting method for realizing a nonrestraintcondition for the vibrator PED5 in FIG. 16. Support members 312a and312b are fixed to the member 302 at positions corresponding to the nodesN1 and N2 of vibration, and are fixed to a support base 311 with asilicone-based adhesive. The overall vibrator may be simply embedded inan adhesive having a relatively low elastic constant.

FIGS. 18A to 23B show a manufacturing process for the piezoelectricvibration angular velocity meter in FIG. 16. A first piezoelectric plateis constituted by a piezoelectric crystal plate 1301 and electrodes 1304and 1306 formed on the upper and lower surfaces of the piezoelectriccrystal plate 1301. A second piezoelectric plate is constituted by apiezoelectric crystal plate 1302 and electrodes 1308 and 1310 formed onthe upper and lower surfaces of the piezoelectric crystal plate 1302.These plates are bonded to each other with an adhesive layer 1307 as ofepoxy resin (FIGS. 18A and 18B). Note that the piezoelectric crystalplates 1301 and 1302 are polarized in the direction of thickness of theelectrode 1304.

In order to maintain high positioning precision in the subsequent steps,the peripheral portion of the joint plate constituted by the theseplates is cut in the direction of thickness with a dicing saw to alignthe side surfaces of the two plates (FIGS. 19A and 19B).

A photoresist 1311 is coated on the electrode 1304. Predetermined areasof the photoresist 1311 are exposed by using an exposure apparatus. Thephotoresist 1311 is exposed such that exposed areas having the samewidth are arranged at equal intervals. The non-exposed areas of thephotoresist 1311 are etched to form a resist pattern corresponding to anelectrode pattern (FIGS. 20A and 20B).

This resist 1311 is used as a protective mask. The exposed portions ofthe silver electrode 1304 are removed by using the reactive ion etching(RIE) method (FIGS. 21A and 21B). Thereafter, the resist 1311 is removed(FIGS. 22A and 22B). As a result, a plurality of strip-like silverelectrodes 1304 are exposed. The joint plate is then cut along adirection perpendicular to the longitudinal direction of the strip-likesilver electrodes 1304 with a dicing saw. In addition, the joint plateis cut along the central line in the longitudinal direction of thesilver electrodes 1304 with the dicing saw (FIGS. 23A and 23B). As aresult, the piezoelectric element shown in FIG. 15 is formed. Accordingto this process, compact bimorph piezoelectric vibration angularvelocity meters can be manufactured in large quantities from one pair ofpiezoelectric plates.

FIG. 24 shows a vibration angular velocity meter PED6 according to thesixth embodiment. This element basically has the same structure as thatof the element shown in FIG. 15. A cross-section of the vibrator PED6 ina direction perpendicular to the longitudinal direction has a width W,in a direction along the surface of an electrode 304, which is smallerthan a side height H in a direction perpendicular to the surface of theelectrode 304. The driving and detection principles of this element arebasically the same as those described with reference to FIGS. 17A to17C. Since the width W in a Coriolis force direction Fc is smaller thanthe height H, the nonrestraint vibration fundamental resonance frequencyin the Coriolis force direction Fc is lower than that in a drivingdirection V.

When an AC voltage having a frequency near the nonrestraint vibrationfundamental resonance frequency in the Coriolis force direction isapplied to a driving piezoelectric member 302 via driving elements 308and 310, vibration is excited in the direction V. The vibration causedat this time causes no resonance because the frequency of the applied ACvoltage is lower than the vibration fundamental basic resonancefrequency. However, since the element PED6 has a bimorph structure, asufficiently large amplitude can be obtained by applying a propervoltage. Detection outer electrodes 304 and 305 are separated from thecentral axis of the vibrator PED6 to maintain the balance of vibrationand prevent coupling of vibration caused by the driving operation in theCoriolis force direction.

When the vibrator rotates about the axis of the vibrator PED6, Coriolisforces are generated. Since the frequency of an AC voltage used for adriving operation is equal to the vibration fundamental resonancefrequency in the Coriolis force direction, a resonant state is set oncethe vibrator is bent by the Coriolis forces. As a result, an amplitudeof a quality factor multiple (sever 10 to several 1,000 times) ofvibration of a static amplitude obtained by piezoelectric strain can beobtained.

Coriolis force signals are detected by the divided electrodes. Thisdetection principle is the same as that in the first embodiment.

If electrodes are two-dimensionally formed on a ceramic plate consistingof a piezoelectric or electrostrictive material, compact vibrators canbe manufactured in large quantities at once. In consideration of such atechnique, there is provided a piezoelectric vibration angular velocitymeter comprising a vibrator having a bimorph structure constituted by afirst member made of a piezoelectric or electrostrictive material in theform of a quadratic prism and a second member made of a piezoelectric orelectrostrictive material in the form of a quadratic prism, an innerelectrode formed between the first and second members, and outerelectrodes formed on the opposite surfaces of the first and secondmembers to the inner electrode.

Bimorph vibrators can be manufactured in large quantities at once byjoining two piezoelectric or electrostrictive plates respectively havingelectrode patterns formed on upper and lower surfaces and having thesame size, and cutting the resultant structure. In addition, if theelectrode patterns are formed by reactive etching, and the joint ceramicplate is cut with a precision cutter, compact bimorph vibrators can bemanufactured with good reproducibility.

Nonrestraint fundamental vibration of a bimorph vibrator is excited byusing a so-called piezoelectric lateral effect by applying a voltagebetween an inner electrode in the bimorph shape as a ground electrodeand the outer electrode on the driving piezoelectric or electrostrictivemember. The vibration, therefore, is caused in a direction perpendicularto the electrode surface. When the vibrator rotates about the axis ofthe vibrator, the vibrator is bent within the electrode surface owing tothe Coriolis forces. This bending due to the Coriolis forces is detectedby the detection piezoelectric or electrostrictive member.

According to the above arrangement, since a piezoelectric signal isgenerated in the Coriolis force detection element upon driving of thevibrator, detection of the Coriolis forces imposes a heavy load on anelectrical system in practice. For this reason, the outer electrode onthe detection piezoelectric or electrostrictive member is divided intotwo electrodes with reference to the central line of the vibrator in theaxial direction. Signals generated in the two electrodes have the samefrequency and opposite phases with respect to the Coriolis forces andare in phase with respect to the driving operation. If, therefore, thedifferential voltages between these signals are obtained, only thesignals almost originating from the Coriolis forces can be obtained.

If a cross-section of the vibrator is square, and the resonancefrequencies in the Coriolis force direction and the driving directioncan be matched with each other, the vibrator can be driven at afrequency near the resonance frequency with a simple oscillation circuitby feeding back outputs from the detection electrodes. Therefore, thevibration based on the Coriolis forces is set in a resonant state, andthe detection sensitivity improves.

In order to omit the cumbersome process of matching resonancefrequencies, the vibrator has a rectangular cross-section tointentionally shift the resonance frequencies in the two directions.With this operation, a bimorph driving operation which allows a largeamplitude without driving the vibrator in a resonant state can berealized, and the frequency of the AC voltage for this driving operationis used as the resonance frequency of the fundamental vibration in theCoriolis force direction. In addition, if the vibrator is driven at afrequency higher than the fundamental resonance frequency in a bimorphdriving operation, vibration cannot be stably caused because of, e.g.,coupling with a high-order mode. For this reason, the vibrator has arectangular cross-section shorter in the electrode surface directionthan in the other direction.

As a method of fixing the vibrator, a method of fixing the vibrator atpositions corresponding to the nodes of nonrestraint fundamentalvibration is most simple and hence preferable.

According to the above method of the present invention, inexpensive,compact vibration angular velocity meters can be provided in largequantities.

FIGS. 26 and 27 show a piezoelectric vibration angular velocity meterPED7 according to the seventh embodiment. This element includesrectangular parallellepiped members 601 and 602 made of a piezoelectricmaterial. Electrodes 605 and 606 are respectively formed on the upperand lower surfaces of the rectangular parallellepiped member 601.Electrodes 608 and 609 are respectively formed on the upper and lowersurfaces of the rectangular parallellepiped member 602. Theserectangular parallellepiped members are fixed to each other with anadhesive layer 607. The electrode 605 on the upper surface is used todetect the strain amount of the element based on Coriolis forces. Thecentral line of the upper-surface electrode 605 in the longitudinaldirection is parallel to the central line of the upper surface of therectangular parallellepiped member 601 in the longitudinal direction butdoes not overlap it.

A support portion 610 has a hole (cavity) OP1 in its center. In thishole OP1, the piezoelectric element is constituted by the rectangularparallellepiped members 601 and 602, the electrodes 606, 608, and 609,and the adhesive layer 607. One end portion of the piezoelectric elementis fitted in the hole OP1 of the support portion 610. The size of theopening of this hole OP1 is almost equal to the area of a cross-sectionof the piezoelectric element in a direction perpendicular to thelongitudinal direction. Although the piezoelectric element and thesupport portion 610 are fixed to each other with an adhesive layer 611,they may be fixed to each other with a screw.

A lead line 606a is electrically connected to the electrodes 606 and608. This lead line 606a is in contact with the inner surface of thehole OP1 of the support portion 610 as well as the electrodes 606 and608. A lead line 605a is electrically connected to the electrode 605.This lead line 605a is in contact with the inner surface of the hole OP1of the support portion 610 as well as the electrode 605. A lead line609a is electrically connected to the electrode 609. The lead line 609ais in contact with the inner surface of the hole OP1 of the supportportion 610 as well as the electrode 609.

FIG. 27 is a sectional view taken along a direction perpendicular to theaxial direction of the vibrator of the vibration angular velocity meterin FIG. 26. A cross-section of the vibrator is almost square, and theresonance frequencies in the vibrator driving direction (indicated by“V” in FIG. 27) and the Coriolis force direction (indicated by “Fc” inFIG. 27) are almost the same. The driving piezoelectric member 602 andthe detection piezoelectric member 601 are respectively polarized in thedirections indicated by arrows PD2 and PD1 in FIG. 27. The electrodes606 and 608 between the two members 601 and 602 are used as groundelectrodes commonly used for driving and detecting operations. When anAC voltage having a frequency near the fundamental resonance frequencyof cantilever vibration is applied to the driving piezoelectric member602, the member 602 tries to expand/contract in accordance with theapplied AC voltage owing to the piezoelectric lateral effect. At thistime, since no driving voltage is applied to the detection piezoelectricmember 601, no force acts on the member to change its length. However,the vibrator obtained by joining the two piezoelectric members becomes aso-called unimorph structure, and resonance of the vibrator is excitedin the direction indicated by “V” in FIG. 27.

In this case, when the vibrator rotates about the vibrator axis, aCoriolis force is generated in the direction indicated by “Fc” in FIG.27, so that the vibrator is bent in a direction perpendicular to boththe vibrator direction and the axial direction of the vibrator. Sincethe resonance frequency in the Coriolis force direction is set to beequal to that in the driving direction, the magnitude of the Coriolisforce, i.e., the rotational angular velocity, can be obtained accordingto equation (1) by detecting a voltage generated in the electrode of thedetection piezoelectric member owing to the piezoelectric lateral effectupon this bending. When the Coriolis force indicated by “Fc” in FIG. 27acts on the vibrator, a compression stress and a tensile stressrespectively act on the left and right sides of the vibrator withrespect to the central axis of the vibrator. In this case, if thedetection electrode is symmetrically arranged with respect to thecentral axis of the vibrator, piezoelectric signals based on thecompression stress and the tensile stress have opposite phases and hencealmost cancel out each other, resulting in low sensitivity. For thisreason, as shown in FIG. 27, the detection electrode 605 is shifted fromthe central axis of the vibrator to allow extraction of only apiezoelectric signal based on a compression or tensile stress upon onebending operation. In this case, a piezoelectric signal based on astress accompanying a driving operation is also generated in thedetection electrode. The signal accompanying the Coriolis force has thesame frequency as that of the driving AC voltage. A signal obtained bysynthesizing the above two signals is obtained from the detectionelectrode.

FIG. 28 shows the basic arrangement of a piezoelectric vibration angularvelocity meter PED8 having a bimorph vibrator according to the eighthembodiment. This vibration angular velocity meter basically has the samemechanism as that shown in FIGS. 26 and 27 except that the detectionelectrode formed on the upper surface of the detection piezoelectricmember is divided into two electrodes (605p and 605q) in the axialdirection of the vibrator.

FIG. 29 is a sectional view taken along a direction perpendicular to theaxis of the vibrator of the vibration angular velocity meter in FIG. 28.A cross-section of the vibrator has a shorter side in the electrodedirection than in a direction perpendicular thereto. The driving anddetection principles are basically the same as those described withreference to FIG. 27. However, the cantilever vibration fundamentalresonance frequency in the Coriolis force direction indicated by “Fc” inFIG. 29 is lower than that in the driving direction indicated by “V” inFIG. 29 because the length of the vibrator in the Coriolis forcedirection is smaller than that in the driving direction.

When an AC voltage having a frequency near the cantilever vibrationfundamental resonance frequency in the Coriolis force direction isapplied to a driving piezoelectric member 602 via a driving electrode609, vibration is excited in the direction indicated by “V” in FIG. 29.The vibration caused at this time does not become resonant vibrationbecause the frequency of the applied AC voltage is lower than thecantilever vibration fundamental resonance frequency in the drivingdirection. However, since the vibrator has a unimorph structure, asufficiently large amplitude can be provided by applying an appropriatevoltage to the driving piezoelectric member 602.

When the vibrator rotates about the axis of the vibrator, a Coriolisforce is generated. Since the frequency of the AC voltage used for adriving operation is equal to the cantilever vibration fundamentalresonance frequency in the Coriolis force direction, a resonant stateoccurs once the vibrator is bent by the Coriolis force. As a result, anamplitude of a quality factor multiple (several 10 to several 1,000times) of vibration of a static amplitude obtained by piezoelectricstrain can be obtained.

A signal based on a Coriolis force is detected by the dividedelectrodes. When the Coriolis force indicated by “Fc” in FIG. 29 acts onthe vibrator, a compression stress and a tensile stress respectively acton the left and right sides of the vibrator with respect to the centralaxis of the vibrator in FIG. 29. Piezoelectric signals obtained from thetwo divided electrodes therefore have the same frequency and oppositephases. Since a signal based on a stress accompanying a drivingoperation of the vibrator is larger than a signal based on a Coriolisforce, it is difficult to detect the Coriolis force from a signalobtained by synthesizing the two signals. For this reason, thedifference (OUT1-OUT2) between signals obtained from the two dividedelectrodes 605p and 605q is detected via leads 1605p and 1605q, and gainand phase adjustment is performed, and the piezoelectric signals basedon the driving operation are canceled out, thereby extracting only thesignal based on the Coriolis force.

Each embodiment described above has exemplified the angular velocitymeter using the vibrator in the form of a quadratic prism. However, asshown in FIGS. 30 and 31 each illustrating a vibrator viewed from theaxial direction of the vibrator, even if a vibrator is in the shape of atriangular prism or column, the operation principle of the vibrationangular velocity meters having the bimorph vibrators of the seventh andeighth embodiments can be used. In either structure, the drivingpiezoelectric member and the detection piezoelectric member are joinedto each other via the ground electrode, and the detection electrode isdivided into two electrodes.

FIG. 30 shows a piezoelectric vibration angular velocity meter PED9according to the ninth embodiment. This element includes a first member732 consisting of a piezoelectric crystal and having three surfaces, andfirst, second, and third electrodes 737a, 737b, and 735 respectivelyformed on the three surfaces.

This element also includes a second member 731 consisting of apiezoelectric crystal and having two parallel surfaces. The secondmember 731 is fixed to the third electrode 735 via one of these twosurfaces. A fourth electrode 736 is formed on the surface of one of thetwo surfaces of the second member 731. These piezoelectric members arerespectively polarized in the directions indicated by arrows PD1 andPD2. The directions indicated by the arrows PD1 and PD2 areperpendicular to the surface of the electrode 735.

An AC voltage is applied between the electrodes 735 and 736. Byobtaining the difference between a voltage signal output across theelectrodes 737a and 735 and a voltage signal output across theelectrodes 737b and 375, the strain amount of this element can bedetected, and hence the angular velocity can be detected.

FIG. 31 shows a piezoelectric vibration angular velocity meter PED10according to the 10th embodiment. This element includes a first member832 consisting of a piezoelectric crystal and having a semicircularcross-section and a second member 831 consisting of a piezoelectriccrystal and having a semicircular cross-section. The second member 831is fixed to the first member 832. The cross-sections of the first andsecond members 832 and 831 constitute a circle. An electrode 835 isinterposed between these members.

An AC voltage is applied between the electrode 835 and an electrode 836.By obtaining the difference between a voltage signal output across anelectrode 837a and the electrode 835 and a voltage signal output acrossan electrode 837b and the electrode 835, the strain amount of thiselement can be detected, and hence the angular velocity can be detected.

If a columnar vibrator is vibrated under cantilever vibration conditionswith one end of the vibrator being fixed, and the other end being set ina nonrestraint state, the vibrator can be easily fixed, and lead linescan be joined to electrode portions on the fixed portion which does notvibrate. Therefore, an almost ideal vibration state can be obtained. Thepresent invention is based on such an idea.

According to the present invention, there is provided a piezoelectricvibration angular velocity meter comprising a columnar vibrator partlyor completely made of a piezoelectric or electrostrictive member, anexcitation means for exciting the vibrator, and a detection means fordetecting a Coriolis force generated in the vibrator, wherein one end ofthe vibrator is fixed.

In addition, the vibrator of the piezoelectric vibration angularvelocity meter of the present invention has a unimorph or bimorphstructure. That is, there is provided a piezoelectric vibration angularvelocity meter comprising a base member made of a metal or ceramicmaterial in the form of a quadratic prism, and a vibrator made of apiezoelectric or electrostrictive material in the form of a quadraticprism and joined to the base member, or a vibrator constituted by afirst member made of a piezoelectric or electrostrictive material in theform of a quadratic prism and a second member made of a piezoelectric orelectrostrictive material in the form of a quadratic prism.

Cantilever vibration allows the vibrator to be easily fixed, and alsoallows lead lines to be connected to the fixed portion which does notvibrate so that an ideal vibration state can be easily attained.

The vibrator preferably has the shape of a quadratic prism, triangularprism, or column because it allows easy adjustment of resonancefrequencies and easy formation of the vibrator.

Driving (excitation) of the vibrator and detection of a Coriolis forceare performed by using the piezoelectric or electrostrictive effect.

In forming a vibrator by using a piezoelectric or electrostrictiveceramic material, a material in the form of a quadratic prism, e.g., aplate-like material, is preferably used because it facilitatespolarization.

When a unimorph vibrator is to be used, a piezoelectric orelectrostrictive element as an excitation means is arranged near thevibrator (on the vibrator or the support portion for fixing thevibrator), and a voltage is applied to the element to excite fundamentalcantilever vibration of the unimorph vibrator.

When a bimorph vibrator is to be used, an inner electrode is used as aground electrode, and a voltage is applied between the inner electrodeand an outer electrode on a piezoelectric or electrostrictive member fora driving operation, i.e., excitation. With this operation, fundamentalcantilever vibration of the bimorph vibrator is excited by using aso-called piezoelectric lateral effect.

In either the unimorph structure or the bimorph structure, vibration iscaused in a direction perpendicular to the electrode surface. When thevibrator rotates about the axis of the vibrator, the vibrator is bentwithin the electrode surface owing to Coriolis forces. Of the signalsgenerated in the two divided outer electrodes for detection, the signalsoriginating from the Coriolis forces have opposite phases, but thesignals originating from the driving operation are in phase. If,therefore, the differential signal between the two signals is obtained,only the signal almost originating from the Coriolis force can beobtained.

If the outer electrode on a piezoelectric or electrostrictive member isdivided into three electrodes, the middle electrode is used forexcitation to execute fundamental cantilever natural oscillation. If theelectrodes on the two sides of the middle electrode are used fordetection, and the differential voltage between the voltages generatedin the two electrodes is obtained, a signal originating from a Coriolisforce can be obtained.

If the vibrator has a square cross-section, and the resonancefrequencies in the Coriolis force direction and the driving directioncan be matched with each other, the vibrator can be driven at afrequency near the resonance frequency with a simple oscillation circuitby feeding back outputs from detection electrodes. Vibration based on aCoriolis force is set in a resonant state to improve the detectionsensitivity.

In order to omit the cumbersome process of matching resonancefrequencies, the vibrator has a rectangular cross-section tointentionally shift the resonance frequencies in the two directions.With this operation, a bimorph driving operation which allows a largeamplitude without driving the vibrator in a resonant state can berealized, and the frequency of the AC voltage for this driving operationis used as the resonance frequency of the fundamental vibration in theCoriolis force direction. In addition, if the vibrator is driven at afrequency higher than the fundamental resonance frequency in a bimorphdriving operation, vibration cannot be stably caused because of, e.g.,coupling with a high-order mode. For this reason, the vibratorpreferably has a rectangular cross-section shorter in the coriolis forcedirection than in the other direction.

In joining two piezoelectric or electrostrictive ceramic plates to eachother, a metal plate as a so-called shim member can be inserted betweenthe two plates to increase the displacement amount of the bimorphstructure.

As described above, according to the present invention, a vibrationangular velocity meter having an ideal vibration state can be easilyprovided.

In addition, inexpensive, compact vibrators can be manufactured in largequantities by forming a plurality of electrode patterns on a largeceramic plate by a printing technique, photolithography, or the like,joining a metal or ceramic plate thereto, and cutting the resultantstructure.

As has been described above, the piezoelectric vibration angularvelocity meter of the present invention includes a columnar unimorph orbimorph vibrator made of a piezoelectric or electrostrictive member, anexcitation electrode for exciting the vibrator, and a detectionelectrode for detecting a Coriolis force generated in the vibrator. Inthe meter, an ideal vibration state can be attained by fixing one end ofthe vibrator.

In the following, a self-excitation circuit which drives a vibrator of apiezoelectric vibrational angular velocity meter or the like in aself-excitation manner will be explained. First, the schematicconfiguration of the self-excitation circuit in accordance with thefollowing embodiments will be explained.

FIG. 55 shows a circuit which is to be compared with the self-excitationcircuit used in the piezoelectric vibrational angular velocity meter ofthe present invention.

This self-excitation circuit is constituted by an inverting amplifier1004 which inversely amplifies a signal from a signal detectingpiezoelectric element 1002 in the upper portion of a vibrator 1001 and alow-pass filter 1005 which adjusts the phase of the output signal of theinverting amplifier 1004. The output side of the low-pass filter 1005 isconnected to a driving piezoelectric element 1003 for the vibrator 1001.

The inverting amplifier 1004 is constituted by an operational amplifier1006 and resistors 1007, 1008, and 1009. The low-pass filter 1005 isconstituted by resistors 1010 and 1011 and capacitors 1012 and 1013 astwo steps of RC filters.

Here, the vibrator 1001 is configured such that piezoelectric elementsare respectively bonded to two side surfaces of a triangle pole made ofa metal. Each of these piezoelectric elements comprises a piezoelectriclayer and electrodes respectively formed on both sides thereof. One ofthese piezoelectric elements is the above-mentioned detectingpiezoelectric element 1002, whereas the other is the above-mentioneddriving piezoelectric element 1003. Also, the above-mentioned trianglepole is grounded.

According to this self-excitation circuit, the signal output from thedetecting electrode 1002 is inversely amplified by the invertingamplifier 1004 and the phase of thus amplified voltage is adjusted bythe low-pass filter 1005, whose output is supplied, as a drivingvoltage, to the driving electrode 1003 of the vibrator 1001.Accordingly, a positive feedback is provided so as to attain a loop gainof 1 or higher, whereby the vibrator 1001 is driven in a self-excitationmanner.

While the vibrator is likely to become mechanically and electricallyunstable, the positively fed-back voltage (driving voltage) may becomeunstable in thus configured self-excitation circuit of FIG. 55 due tothe mechanical and electrical unstableness of the vibrator 1001.Accordingly, it may not prevent such problems as unstable amplitude uponself-excited vibration of the vibrator and abnormal oscillation atfrequencies other than the resonance frequency of the vibrator fromoccurring.

The following self-excitation circuits and the piezoelectric vibrationalangular velocity meter using the same can stabilize driving voltageregardless of the mechanical and electrical unstableness of thevibrator, thereby stabilizing the amplitude at the self-excitationvibration of the vibrator while preventing the abnormal oscillation atfrequencies other than the resonance frequency of the vibrator fromoccurring.

First, the outline of the following embodiments will be explained.

The self-excitation circuit of the first embodiment is a self-excitationcircuit for driving a vibrator in a self-excitation manner and comprisesa converting means for converting a first sine wave voltage indicativeof a state of vibration of the vibrator into a square wave voltage whichbecomes a first predetermined level when the first square wave voltageis greater than a predetermined reference level while becoming a secondpredetermined level when the first square wave voltage is smaller thanthe predetermined reference level; a filter for filtering a second sinewave voltage, which has a frequency identical to that of the first sinewave voltage, from the square wave voltage; and a phase shifter foradjusting the phase of the second sine wave voltage, which has beenfiltered by the filter, such that the amplitude of vibration of thevibrator is substantially maximized.

The self-excitation circuit of the second embodiment comprises acurrent/voltage converter which receives one input signal from thevibrator as an electric current signal and converts the electric currentsignal into a voltage signal, while the converting means converts theoutput of the current/voltage converter, as the first sine wave voltage,into the square wave voltage.

The self-excitation circuit of the third embodiment comprises a meansfor receiving one input signal from the vibrator as a voltage signal,while the converting means converts this voltage signal, as the firstsine wave voltage, into the square wave voltage.

The self-excitation circuit of the fourth embodiment comprises a meansfor receiving a plurality of input signals from the vibrator andattaining a voltage signal corresponding to the sum of the plurality ofinput signals, while the converting means converts the voltage signalcorresponding to the sum of the plurality of input signals, as the firstsine wave voltage, into the square wave voltage.

In the self-excitation circuit of the fifth embodiment, the means forattaining a voltage signal corresponding to the sum of the plurality ofinput signals has a plurality of current/voltage converters whichrespectively receive the plurality of input signals as electric currentsignals and convert these electric current signals into voltage signals.

In the self-excitation circuit of the sixth embodiment, the means forattaining a voltage signal corresponding to the sum of the plurality ofinput signals has a means for receiving the plurality of input signalsrespectively as voltage signals.

In the self-excitation circuit of the seventh embodiment, the convertingmeans includes a zero-cross comparator.

The self-excitation circuit of the eighth embodiment further comprisesan attenuator 1042 for attenuating the output of the zero-crosscomparator.

In the self-excitation circuit of the ninth embodiment, the attenuatorcomprises a potential dividing circuit including a variable resistor.

The piezoelectric vibrational angular velocity meter of the tenthembodiment comprises a vibrator and a self-excitation circuit fordriving the vibrator in a self-excitation manner.

In the piezoelectric vibrational angular velocity meter of the eleventhembodiment, the vibrator in the tenth embodiment comprises first andsecond members each made of a rectangular parallelopiped piezoelectricmember; a first electrode formed between a first side surface of thefirst member and a first side surface of the second member; second andthird electrodes 1033 and 1034 respectively formed at both sidepositions on a second side surface of the first member opposite to thefirst side surface thereof or respectively formed on third and fourthside surfaces of the first member neighboring the first side surfacethereof; and a fourth electrode 1035 formed on a second side surface ofthe second member opposite to the first side surface thereof.

In the piezoelectric vibrational angular velocity meter of the twelfthembodiment, the vibrator in the eleventh embodiment further comprises afifth electrode formed at substantially the center position of thesecond side surface of the first member.

In the piezoelectric vibrational angular velocity meter of thethirteenth embodiment, the vibrator in the tenth embodiment comprises amember made of a columnar piezoelectric material and a plurality ofband-like electrodes formed on the outer peripheral surface of thismember so as to extend in the axial direction thereof.

In the piezoelectric vibrational angular velocity meter of thefourteenth embodiment, the vibrator in the tenth embodiment comprises amember made of a metal formed like a polygonal (higher than triangle)pole and a plurality of piezoelectric elements respectively bonded to aplurality of side surfaces of the member.

The above-mentioned converting means converts the first sine wavevoltage indicative of the state of vibration of the vibrator into asquare wave voltage having a predetermined level. The first sine wavevoltage is obtained on the basis of one or a plurality of input signalsfrom the vibrator. While the amplitude of the first sine wave voltagemay fluctuate due to mechanical and electrical unstableness of thevibrator, the level of the square wave voltage is always maintained atthe predetermined level. From the square wave voltage, the second sinewave voltage having a frequency identical to that of the first sine wavevoltage is filtered by the filter. Accordingly, regardless of thefluctuation in amplitude of the first sine wave voltage, namely,regardless of the mechanical and electrical unstableness of thevibrator, the amplitude of the second sine wave voltage is securely heldat a predetermined level. Then, the phase of the second sine wavevoltage is adjusted by the phase shifter such that the amplitude ofvibration of the vibrator is substantially maximized. The output of thephase shifter is supplied, as a driving voltage, to the vibrator so asto provide a positive feedback. Consequently, the vibrator is driven ina self-excitation manner.

Accordingly, regardless of the mechanical and electrical unstableness ofthe vibrator, the amplitude of the driving voltage supplied to thevibrator is held at a predetermined level and stabilized. Therefore, theamplitude of the self-excited vibration of the vibrator is stabilized,thereby preventing the vibrator from abnormally oscillating atfrequencies other than the resonance frequency thereof.

When the vibrator configured in accordance with the eleventh or twelfthembodiment is adopted as the vibrator, a large number of such vibratorscan be made at once, for example, when two sheets of piezoelectricplates in which electrode patterns have been formed on both sidesthereof are bonded together and then cut. Also, when the electrodepatterns are formed by reactive etching or the like and the bondedplates are cut by a precision cutting machine or the like, smallvibrators can be made with a favorable reproducibility.

In the following, self-excitation circuits in accordance withembodiments will be explained in further detail with reference to thedrawings. FIG. 32 shows a self-excitation circuit in accordance with anembodiment. The piezoelectric vibrational angular velocity meter inaccordance with this embodiment comprises, as shown in FIG. 32, avibrator 1020, a self-excitation circuit 1021 for driving the vibrator1020 in a self-excitation manner, and a detection circuit 1022 whichattains, based on an input signal from the vibrator 1020, a detectionsignal corresponding to Coriolis force acting on the vibrator 1020.

First, the vibrator 1020 will be explained with reference to FIGS. 33and 34. FIG. 33 is a perspective view of the vibrator 1020, whereas FIG.34 is a front view thereof.

As shown in FIG. 33, the vibrator 1020 comprises first and secondmembers 1030 and 1031 each made of a piezoelectric material formed likea rectangular parallelopiped (which may not strictly be a rectangularparallelopiped), an electrode 1032 formed between a first side surface(lower surface in FIG. 34) of the first member 1030 and a first sidesurface (upper surface in FIG. 34) of the second member 1031, electrodes1033 and 1034 respectively formed at both side positions on a secondside surface (upper surface in FIG. 34) of the first member 1030opposite to the first side surface thereof, and an electrode 1035 formedon a second side surface (lower surface in FIG. 34) of the second member1031 opposite to the first side surface thereof.

In this embodiment, each of the first and second members 1030 and 1031is made of a piezoelectric ceramic (e.g., lead zirconate titanate (PZT))and has a thickness of 0.5 mm, a width of 1.0 mm, and a length of 9.0mm. The present invention, however, should not be restricted to such asize. The direction of polarization of the first member 1030 is theupward direction in FIG. 34, whereas that of the second member 1031 isthe downward direction in FIG. 34. The electrodes 1033 and 1034 arerespectively formed, by silver paste, at both side positions on theupper surface of the first member 1030 so as to extend in thelongitudinal direction of the first member 1030 each with a width of 0.3mm. The electrode 1035 is formed by silver paste on the whole lowersurface of the second member 1031. The electrode 1032 is configured suchthat silver paste formed on the whole lower surface of the first member1030 beforehand and silver paste formed on the whole upper surface ofthe second member 1031 beforehand are bonded together by means of anadhesive such as an epoxy adhesive (not depicted). In order to minimizethe influence of the adhesive upon the vibration of the vibrator, anadhesive having a low viscosity is preferably used therefor. Here, evenwhen the adhesive itself does not have any conductivity, there are anumber of minute areas between the silver paste formed on the lowersurface of the first member 1030 and the silver paste formed on theupper surface of the second member 1031 which are directly brought intocontact with each other without intervention of the adhesive when anappropriate pressure is applied thereto at the time of bonding, therebyelectrically connecting with each other. Of course, a conductiveadhesive may be used therefor.

Since the vibrator 1020 is thus configured, a large number of suchvibrators can be made at once. Namely, when a piezoelectric plate inwhich a number of electrode patterns for the electrodes 1033 and 1034and a number of electrode patterns constituting a part of the electrode1032 have been formed for the number of vibrators 1020 beforehand and apiezoelectric plate in which a number of electrode patterns for theelectrode 1035 and a number of electrode patterns constituting the otherpart of the electrode 1032 have been formed for the number of vibrators1020 beforehand are bonded together by means of the above-mentionedadhesive and then cut into the individual vibrators 1020, the largenumber of vibrators 1020 can be made at once. Also, when the electrodepattern formation by reactive etching or the like and the cutting of thebonded plates by a precision cutting machine or the like are effected,the vibrator 1020 having a small size can be made with a favorablereproducibility.

In this vibrator 1020, for example, the electrode 1032 is used as areference electrode (earth electrode), the electrodes 1033 and 1034 areused as Coriolis force detecting electrodes, and the electrode 1035 isused as a vibrator excitation electrode (driving electrode). Also, oneor both of the electrodes 1033 and 1034 are used for taking out theinput signal for the self-excitation circuit, namely, used for takingout the signal for attaining a voltage indicative of the state ofvibration of the vibrator 1020 for self-excitation. When an excitationvoltage is applied to the electrode 1035 while using the electrode 1032as a reference electrode, the second member 1031 is subjected to bendingvibration in a direction (vertical direction in FIG. 34) perpendicularto the surfaces of the electrodes 1032 and 1035, whereby the vibrator1020 as a whole is subjected to bending vibration in this direction.Assuming that the vibrator 1020 is rotated around an arbitrary axiswhich extends in the longitudinal direction of the members 1030 and1031, Coriolis force is generated in the width direction of the members1030 and 1031, whereby refracting vibration of the vibrator 1020 occursin this direction due to the Coriolis force. Due to this refractingvibration, signals corresponding to the Coriolis force are generated atthe electrodes 1033 and 1034, respectively, in phases opposite to eachother. Though the signals generated at the electrodes 1032 and 1034include not only these signals but also the signals due to the bendingvibration (excitation) of the vibrator 1020 in the directionperpendicular to the surfaces of the electrodes 1032 and 1035, thesignal corresponding to the Coriolis force can be obtained alone whenthe differential between the signal of the electrode 1033 and the signalof the electrode 1034 is determined so as to cancel the component due tothe excitation. As a result, the rotational speed (angular velocity) ofthe vibrator 1020 can be measured.

Here, as the material for each of the members 1030 and 1031, apiezoelectric material having a large Q value is selected in order forthe vibrator 1020 to efficiently vibrate upon application of the drivingvoltage thereto and to generate a high voltage due to the vibrationthereof. Also, it is preferable for the vibrator 1020 to have resonancefrequencies in its thickness direction and width directionssubstantially coincide with each other. When they coincide with eachother, the vibrator 1020 has a substantially square cross section. Forexample, this frequency matching operation is effected as, while thevibrator 1020 is vibrated, its side surface is shaven with laser or thelike so as to adjust the resonance frequency.

Next, with reference to FIGS. 32 and 35, the self-excitation circuit1021 will be explained. FIG. 35 is a waveform chart showing waveforms atpoints a to e in FIG. 32.

As shown in FIG. 32, the self-excitation circuit 1021 comprises acurrent/voltage converter (I-V converter) 1040, a zero-cross comparator1041, attenuator 1042, a band-pass filter 1043, and a phase shifter1044.

The input side of the current/voltage converter 1040 acts as an inputterminal of the self-excitation circuit 1021 and is connected to theelectrode 1033 (which may be the electrode 1034, of course) of thevibrator 1020. When a sine wave AC voltage with the resonance frequencyof the vibrator 1020 is applied (by a voltage follower constituted by anoperational amplifier 1072 as will be explained later) between theelectrode 1035 and the electrode 1032, the vibrator 1020 vibrates in adirection perpendicular to the surfaces of the electrodes 1032 and 1035.Upon this vibration, a sine wave with the resonance frequency of thevibrator 1020 is generated from the electrodes 1033 and 1034 due to apiezoelectric effect.

As shown in FIG. 32, the current/voltage converter 1040 is constitutedby an operational amplifier 1051, a resistor 1052, and a capacitor 1053.The input side of the current/voltage converter 1040 is connected to theelectrode 1033 of the vibrator 1020 such that one input signal (signalfrom the electrode 1033 in this embodiment) of the vibrator 1020 isreceived as an electric current signal which is then converted into andoutput as a voltage signal. Namely, in this embodiment, as the vibrator1020 vibrates, an electric charge generated upon its piezoelectriceffect flows into a virtual grounding point of the operational amplifier1051 by way of the electrode 1033, whereby its current is converted intoa voltage. Since the piezoelectric signal from the vibrator 1020 is thustaken out as an electric current signal in this embodiment, thepiezoelectric signal can be collected without loss. In this embodiment,the phase of the input current and the phase of the output voltage areinverted with respect to each other. Also, the resistor 1052 and thecapacitor 1053 constitute a low-pass filter, which cuts a high frequencycomponent. The capacitor 1053 may be omitted, however.

The voltage signal (sine wave voltage) output from the current/voltageconverter 1040 is shown in (a) of FIG. 35. As indicated by continuouscurve and dotted curve in (a), when an angular velocity is imparted tothe vibrator 1020 so as to generate Coriolis force, for example, theamplitude of the output of the current/voltage converter 1040 inevitablychanges in response thereto. Also, the amplitude of the output of thecurrent/voltage converter 1040 fluctuates due to the mechanical andelectrical unstableness of the vibrator 1020.

The zero-cross comparator 1041 is constituted by means of an operationalamplifier 1054 and converts the output (which corresponds to the sinewave voltage indicative of the state of vibration of the vibrator 1020in this embodiment) of the current/voltage converter 1040 into a squarewave voltage which has a positive power source voltage level (e.g., +3V) when the output of the current/voltage converter 1040 is greater thanzero level (potential of the electrode 1032) while having a negativepower source voltage level (e.g., −3 V) when the output of thecurrent/voltage converter 1040 is smaller than zero level. In this case,regardless of the amplitude of the input waveform, the square wavevoltage is output with its amplitude being securely set by thezero-cross comparator 1041 at an output amplitude determined by thepower source voltage. In FIG. 35, (b) shows the output of the zero-crosscomparator 1041. Though the zero-cross comparator 1041 is used while thereference level is set at zero level such that the square wave voltagehas no DC component in this embodiment, the square wave voltage may havea DC component.

The attenuator 1042 is constituted by a potential dividing circuitcomposed of a resistor 1055 and a variable resistor 1056 and outputs theoutput (square wave voltage) of the zero-cross comparator 1041 with itsamplitude being attenuated according to the potential dividing ratiothereof. The amplitude of the square wave voltage output from theattenuator 1042 can be arbitrarily set as the variable resistor 1056 isadjusted. The output of the attenuator 1042 is shown in (c) of FIG. 35.As the amplitude of the output voltage of the attenuator 1042 isdecreasingly adjusted by the variable resistor 1056 therein, the voltage(driving voltage) imparting a positive feedback to the electrode 1035,which will be explained later, becomes constant, thereby enabling thevibrator 1020 to be subjected to self-excitation with a constantamplitude. Here, when the amplitude of the square wave voltage outputfrom the zero-cross comparator 1041 is appropriate, the attenuator 1042may be omitted.

The band-pass filter 1043 is a state variable filter constituted byoperational amplifiers 1057 to 1059, resistors 1060 to 1065, and acapacitor 1066 and only transmits therethrough frequencies near theresonance frequency of the vibrator 1020. Namely, from the square wavevoltage output from the attenuator 1042, the band-pass filter 1043filters the sine wave voltage having a frequency identical to that ofthe output voltage of the current/voltage converter 1040. In thisembodiment, with respect to the input square wave voltage output fromthe attenuator 1042, the band-pass filter 1043 outputs a sine wavevoltage having an inverted phase (due to the fact that the phases of theinput current and the output voltage are inverted by the current/voltageconverter 1040) and a constant amplitude with the resonance frequency ofthe vibrator 1020. Its output waveform is shown in (d) of FIG. 35. Inplace of the band-pass filter 1043, a low-pass filter may be used. Thepassing band of the band-pass filter 1043 is determined by resistancevalues of the resistors 1060 to 1065.

As shown in (d) of FIG. 35, the phase of the sine wave voltage outputfrom the band-pass filter 1043 is shifted and, in general, slightlyretarded from the phase at which the amplitude of the vibration of thevibrator 1020 is substantially maximized.

The phase shifter 1044 adjusts the phase of the sine wave voltage, whichhas been filtered by the band-pass filter 1043, such that the amplitudeof the vibration of the vibrator 1020 is substantially maximized. Itsoutput waveform is shown in (e) of FIG. 35. In this embodiment, theband-pass filter 1043 is constituted by an operational amplifier 1067,resistors 1068 and 1069, a variable resistor 1070, and a capacitor 1075,such that the phase of the output waveform can be minutely adjusted asthe resistance value of the variable resistor 1070 is adjusted. Though avoltage follower composed of an operational amplifier 1071 is providedbetween the output side of the band-pass filter 1043 and the input sideof the phase shifter 1044 in this embodiment, it may be omitted.

To the output side of the phase shifter 1044, the input side of thevoltage follower composed of the operational amplifier 1072 isconnected, while the output side of this voltage follower acts as theoutput terminal of the self-excitation circuit 1021, which is connectedto the electrode 1035 of the vibrator 1020. Accordingly, the output ofthe phase shifter 1044 is supplied to the electrode 1035 by way of thevoltage follower so as to provide a positive feedback with the resonancefrequency of the vibrator 1020, whereby the vibrator 1020 can beefficiently and correctly driven in a self-excitation manner. Here, thevoltage follower composed of the operational amplifier 1072 may beomitted as well, thereby making the output side of the phase shifter1044 as the output terminal of the self-excitation circuit 1021.

The configurations of the current/voltage converter 1040, zero-crosscomparator 1041, attenuator 1042, filter 1043, and phase shifter 1044should not be restricted to those mentioned above, however.

According to the self-excitation circuit 1021 explained in theforegoing, regardless of the fluctuation in the amplitude of the sinewave voltage ((a) in FIG. 35) which is the output of the current/voltageconverter 1040 and indicative of the state of vibration of the vibrator1020, namely, regardless of the mechanical and electrical unstablenessof the vibrator and the influence of Coriolis force, the amplitude ofthe sine wave voltage (driving voltage), which is the output of thephase shifter 1044 and used as a driving voltage, is securely set to apredetermined level and stabilized. Accordingly, the amplitude of theself-excited vibration of the vibrator 1020 is stabilized, therebypreventing the vibrator 1020 from abnormally oscillating at frequenciesother than the resonance frequency thereof.

In the following, with reference to FIG. 32 again, the detection circuit1022 will be explained. In this embodiment, the detection circuit 1022comprises a current/voltage converter 1080 and a differential circuit1081, while the current/voltage converter 1040 is also commonly used aspart of the detection circuit 1022. As in the case of thecurrent/voltage converter 1040, the current/voltage converter 1080 isconstituted by an operational amplifier 1082, a resistor 1083, and acapacitor 1084. The input side of the current/voltage converter 1080 isconnected to the electrode 1034 of the vibrator 1020. The differentialcircuit 1081 takes out the differential between the outputs of thecurrent/voltage converters 1040 and 1080 and outputs this differential.As can be seen from the explanation previously provided in conjunctionwith the vibrator 1020, the output of the differential circuit 1081becomes the signal corresponding to the Coriolis force, namely, thedetection signal.

FIG. 36 is a circuit diagram showing a piezoelectric vibrational angularvelocity meter in accordance with another embodiment. In FIG. 36,constituents identical or corresponding to those shown in FIG. 32 arereferred to with marks identical thereto without repeating theirexplanations.

The piezoelectric vibrational angular velocity meter shown in FIG. 36differs from that shown in FIG. 32 mentioned above only in the followingpoints. Namely, while the electric current signal is taken out by thecurrent/voltage converter 1040 from only one electrode 1033 in theelectrodes 1033 and 1034 of the vibrator 1020 and then converted into avoltage signal so as to be directly input into the zero-cross comparator1041 in the self-excitation circuit 1021 of the piezoelectricvibrational angular velocity meter shown in FIG. 32, the current/voltageconverter 1080 of the detection circuit 1022 is commonly used such thatthe electric current signals are respectively taken out from theelectrodes 1033 and 1034 of the vibrator 1020 by the current/voltageconverters 1040 and 1080 and then converted into voltage signals, whosesum (corresponding to the sine wave voltage indicative of the state ofvibration of the vibrator 1020 in this embodiment) is formed by an adder1090 and then input into the zero-cross comparator 1041 in aself-excitation circuit 1100 of the piezoelectric vibrational angularvelocity meter shown in FIG. 36. Though the adder 1090 is constituted byresistors 1091 and 1092 in this embodiment, it should not be restrictedthereto.

Since the signals corresponding to Coriolis force are generated at theelectrodes 1033 and 1034 with phases opposite to each other, the voltagesignals output from the respective current/voltage converters 1040 and1080 are sine waves whose amplitudes change due to the Coriolis force inphases opposite to each other. Accordingly, when the sum of theiroutputs is formed by the adder 1090, their changes are supposed to beoffset against each other, thereby making a constant output regardlessof the Coriolis force. Actually, however, due to a slight differencebetween the areas of the electrodes 1033 and 1034, local positionaldifferences in characteristics of PZT, and other mechanical andelectrical unstableness of the vibrator 1020, the output (sum output) ofthe adder 1090 may not become constant, whereby the amplitude in theoutput of the adder 1090 may fluctuate.

However, the sine wave voltage signal having thus changed amplitude isinput into the zero-cross comparator 1041 such that its output isconverted into a rectangular voltage whose amplitude is determined bythe power source voltage and thereby does not depend on the amplitudeoutput of the input. The functions of the attenuator 1042, band-passfilter 1043, and phase shifter 1044 subsequent thereto are the same asthose in the case of the self-excitation circuit 1021 shown in FIG. 32.

Accordingly, also in this embodiment, the amplitude of the self-excitedvibration of the vibrator 1020 is stabilized, thereby preventing thevibrator 1020 from oscillating at frequencies other than the resonancefrequency thereof.

In the following, a piezoelectric vibrational angular velocity meter inaccordance with another embodiment will be explained with reference toFIG. 37. FIG. 37 is a circuit diagram showing the piezoelectricvibrational angular velocity meter in accordance with this embodiment.In FIG. 37, constituents identical or corresponding to those shown inFIG. 32 are referred to with marks identical thereto without repeatingtheir explanations.

The piezoelectric vibrational angular velocity meter shown in FIG. 37differs from that shown in FIG. 32 mentioned above only in the followingpoints. Namely, while the input signal from the electrode 1033 of thevibrator 1020 is taken out by the current/voltage converter 1040 as anelectric current signal so as to be converted into a voltage signal inthe self-excitation circuit 1021 in the piezoelectric angular velocitymeter shown in FIG. 32, the input signal from the electrode 1033 of thevibrator 1020 is taken out as a voltage signal by way of a resistor 1105so as to be input into the zero-cross comparator 1041 in aself-excitation circuit 1110 in the piezoelectric angular velocity metershown in FIG. 37. Also, consequently, a detection circuit 1120 shown inFIG. 37 takes out the input signal from the electrode 1034 as a voltagesignal by way of a resistor 1106. The differential circuit 1081 takesout the differential between the voltage signals from the resistors 1105and 1106. While the phases of the input electric current and outputvoltage are inverted with respect to each other in the current/voltageconverter 1040 in the self-excitation circuit 1021 in the piezoelectricangular velocity meter shown in FIG. 32, no such inversion of phasesoccurs in the self-excitation circuit 1110 in the piezoelectric angularvelocity meter shown in FIG. 37. Accordingly, the amount of phaseadjustment in the phase shifter 1044 in FIG. 37 differs from that inFIG. 32.

Accordingly, also in this embodiment, the amplitude of the self-excitedvibration of the vibrator 1020 is stabilized, thereby preventing thevibrator 1020 from oscillating at frequencies other than the resonancefrequency thereof.

In the following, a piezoelectric vibrational angular velocity meter inaccordance with another embodiment will be explained with reference toFIG. 38. FIG. 38 is a circuit diagram showing the piezoelectricvibrational angular velocity meter in accordance with this embodiment.In FIG. 38, constituents identical or corresponding to those shown inFIG. 32 are referred to with marks identical thereto without repeatingtheir explanations.

The piezoelectric vibrational angular velocity meter shown in FIG. 38differs from that shown in FIG. 36 mentioned above only in the followingpoints. Namely, while the current/voltage converters 1040 and 1080 areused to respectively take out the input signals from the electrodes 1033and 1034 of the vibrator 1020 as current signals and then convert theminto voltage signals whose sum is input into the zero-cross comparator1041 by the adder 1090 in the self-excitation circuit 1100 in thepiezoelectric vibrational angular velocity meter shown in FIG. 36, anadder 1131 is used to take out input signals from the electrodes 1033and 1034 of the vibrator 1020 as voltage signals whose sum is input intothe zero-cross comparator 1041 in a self-excitation circuit 1130 in thepiezoelectric vibrational angular velocity meter shown in FIG. 38. Also,consequently, in a detection circuit 1140 in FIG. 38, the input signalsfrom the electrodes 1033 and 1034 of the vibrator 1020 are respectivelytaken out as voltage signals by way of resistors 1141 and 1142, while adifferential circuit 1081 takes out the differential between the voltagesignals from the resistors 1141 and 1142. Though the adder 1131 isconstituted by an operational amplifier 1132 and resistors 1133 to 1135in this embodiment, it should not be restricted thereto. In this adder1131, the input voltage and output voltage have phases inverted withrespect to each other.

Next, another example of vibrators used in the piezoelectric vibrationalangular velocity meter in accordance with the present invention will beexplained with reference to FIGS. 39 and 40. FIG. 39 is a perspectiveview of this vibrator 1200, whereas FIG. 40 is a front view thereof. InFIGS. 39 and 40, constituents identical to those shown in FIG. 33 arereferred to with marks identical thereto without repeating theirexplanations.

This vibrator 1200 differs from the vibrator 1020 shown in FIG. 33 onlyin that an electrode 1201 is additionally provided in the vibrator 1200.Namely, in the vibrator 1200, at substantially the center position inthe second side surface (upper surface in FIG. 40) of the first member1030, the electrode 1201 is formed independently from the electrodes1033 and 1034. In this example, the electrode 1201 is formed by silverpaste at the center of the upper surface of the first member 1030 so asto extend in the longitudinal direction thereof with a width of 0.3 mm.Since the electrode 1201 is formed at the center of the upper surface ofthe first member 1030, its voltage does not fluctuate upon bendingvibration of the members 1030 and 1031 in their width direction due toCoriolis force. Also, since it is independent from the electrodes 1033and 1034, the detection circuit and the self-excitation circuit can beelectrically separated from each other, thereby preventing them frominterfering with each other.

This vibrator 1200 can be combined with the self-excitation circuits1021 and 1110 shown in FIGS. 32 and 37, for example. When the vibrator1200 is combined with the self-excitation circuit 1021 shown in FIG. 32,for example, the electrode 1201 of the vibrator 1200 is connected to theinput side of the current/voltage converter 1040, while the electrode1035 of the vibrator 1200 is connected to the output side of the voltagefollower 1072. Also, the electrode 1034 of the vibrator 1200 isconnected to the input side of the current/voltage converter 1080 of thedetection circuit 1022, while a current/voltage converter (notdepicted), which is similar to the current/voltage converter 1080, isadded to the detection circuit 1022. The electrode 1033 of the vibrator1200 is connected to the input side of thus added current/voltageconverter. The differential circuit 1081 takes out the differentialbetween the output of the current/voltage converter 1080 and the outputof the added current/voltage converter. Similarly, the vibrator 1200 maybe combined with the self-excitation circuit 1110 shown in FIG. 37.

Also, in the piezoelectric vibrational angular velocity meters shown inFIGS. 32, 36, 37, and 38, a vibrator 1210 shown in FIG. 41 may be usedin place of the vibrator 1020 shown in FIG. 33.

FIG. 41 is a perspective view of this vibrator 1210, whereas FIG. 42 isa front view thereof. In FIG. 41, constituents identical orcorresponding to those shown in FIG. 33 are referred to with marksidentical thereto without repeating their explanations.

This vibrator 1210 differs from the vibrator 1020 only in that theelectrodes 1033 and 1034 are not formed on the upper surface (secondsurface) of the first member 1030 but respectively formed at the thirdand fourth side surfaces of the first member 1030 neighboring the firstside surface (lower surface) of the first member 1030. It is clear thatthe vibrator 1210 is substantially equivalent to the vibrator 1020.

As in the case of the vibrator 1200 shown in FIG. 39, a vibrator 1220shown in FIGS. 43 and 44 may be combined with the self-excitationcircuits 1021 and 1110 respectively shown in FIGS. 32 and 37.

FIG. 43 is a perspective view of this vibrator 1220, whereas FIG. 44 isa front view thereof. In FIG. 43, constituents identical orcorresponding to those shown in FIG. 39 are referred to with marksidentical thereto without repeating their explanations.

This vibrator 1220 differs from the vibrator 1200 shown in FIG. 39 onlyin that the electrodes 1033 and 1034 are not formed on the upper surface(second surface) of the first member 1030 but respectively formed at thethird and fourth side surfaces of the first member 1030 neighboring thefirst side surface (lower surface) of the first member 1030. It is clearthat the vibrator 1220 is substantially equivalent to the vibrator 1200.

Also, in the piezoelectric vibrational angular velocity meters shown inFIGS. 32, 36, 37, and 38, a vibrator 1230 shown in FIG. 45 may be usedin place of the vibrator 1020 shown in FIG. 33.

FIG. 45 is a perspective view of this vibrator 1230, whereas FIG. 46 isa front view thereof. In FIG. 45, constituents identical to those shownin FIG. 33 are referred to with marks identical thereto withoutrepeating their explanations.

This vibrator 1230 differs from the vibrator 1020 only in that theelectrode 1035 formed on the second side surface (lower surface in FIG.46) of the second member 1031 in the vibrator 1020 is omitted and anelectrode 1231 is added thereto instead. The electrode 1231 is formed bysilver paste at substantially the center position of the second sidesurface (upper surface in FIG. 46) of the first member 1030 so as toextend in the longitudinal direction of the first member 1030 with awidth larger than that of each of the electrodes 1033 and 1034.

While the vibrator 1020 shown in FIG. 33 utilizes the piezoelectricphenomenon of the second member 1031 to excite the vibrator 1020 as awhole, the vibrator 1230 shown in FIG. 45 does not utilize thepiezoelectric phenomenon of the second member 1031 at all but utilizesthe piezoelectric phenomenon of the first member 1030 alone to not onlydetect the vibration of the vibrator 1230 but also excite the vibrator1230 as a whole. Nevertheless, the vibrator 1230 is similar to thevibrator 1020.

Since the vibrator 1230 does not utilize the piezoelectric phenomenon ofthe second member 1031 at all and thus the second member 1031 ispiezoelectrically inactive, not only piezoelectric materials but alsoinherently piezoelectrically inactive materials such as alumina andglass may be used as the material for the second member 1031.

When this vibrator 1230 is used in the piezoelectric vibrational angularvelocity meters shown in FIGS. 32, 36, 37, and 38 in place of thevibrator 1020 shown in FIG. 33, the output terminal of each of theself-excitation circuits 1021, 1100, 1110, and 1130 is connected to theelectrode 1231 of the vibrator 1230.

Also, in the piezoelectric vibrational angular velocity meters shown inFIGS. 32, 36, 37, and 38, a vibrator 1240 shown in FIGS. 47 and 48 maybe used in place of the vibrator 1020 shown in FIG. 33.

FIG. 47 is a perspective view of this vibrator 1240, whereas FIG. 48 isa front view thereof. In FIG. 47, constituents identical orcorresponding to those shown in FIG. 45 are referred to with marksidentical thereto without repeating their explanations.

This vibrator 1240 differs from the vibrator 1230 shown in FIG. 45 onlyin that the electrodes 1033 and 1034 are not formed on the upper surface(second surface) of the first member 1030 but respectively formed at thethird and fourth side surfaces of the first member 1030 neighboring thefirst side surface (lower surface) of the first member 1030. It is clearthat the vibrator 1240 is substantially equivalent to the vibrator 1230.

In the following, a still another example of the vibrator used in thepiezoelectric vibrational angular velocity meter in accordance with thepresent invention will be explained with reference to FIG. 49. FIG. 49is a perspective view of this vibrator 1300, whereas FIG. 50 is a frontview thereof.

In this vibrator 1300, PZT plates (i.e., piezoelectric elements) 1320,1330, 1340, and 1350, each of which has a length of 1.6 mm, a width of 3mm, and a thickness of 0.3 mm with electrodes (not depicted) formed bysilver paste on both sides thereof are respectively bonded to four sidesurfaces of a metal pole (column) 1310 made of an elinvar alloy having asquare cross section, whose each side is 2 mm, with a length of 15 mm.The sizes of the respective portions should not be restricted to thosementioned above, however.

The PZT plate 1320 is used for exciting the vibrator by an inversepiezoelectric effect, whereas the PZT plate 1330 is used for generatinga voltage upon vibration of the vibrator 1300 due to a piezoelectriceffect. The PZT plates 1340 and 1350 are used for sensing Coriolis forcegenerated when the vibrator is rotated around an axis which is inparallel to the longitudinal direction thereof so as to have an angularvelocity. As the metal pole 1310 is used as an earth electrode, theelectrode at the surface of each of the PZT plates 1320, 1330, 1340, and1350 in contact with the metal pole 1310 has an earth potential. The PZTplate 1320 vibrates due to the sine wave voltage applied thereto. Uponthis vibration, the metal pole 1310 vibrates so as to formirregularities in the thickness direction of the PZT plate 1320. The PZTplate 1330 vibrates so as to follow the metal pole 1310, whereby avoltage having a frequency identical to that of the vibration isgenerated due to a voltage effect. At the Coriolis vibration sensingelectrodes 1340 and 1350, voltages corresponding to the Coriolis forceare generated in phases inverted with respect to each other withfrequencies identical to each other and identical to the frequency ofthe vibrator.

In the case of this vibrator 1300, the self-excitation circuits shown inFIGS. 32, 36, 37, and 38 may be used. The metal pole 1310, the outerelectrodes of the PZT plates 1350 and 1340, and the outer electrode ofthe PZT plate 1320 may be respectively used as the electrode 1032,electrodes 1033 and 1034, and electrode 1035 of the vibrator 1020. Also,in the case of the self-excitation circuits shown in FIGS. 32 and 38,namely, when one of the PZT plates 1340 and 1350 is used as thecomparator input, a similar self-excited driving operation can beeffected when the output of the PZT plate 1330 is used in place thereof.

In the following, a still another example of the vibrator used in thepiezoelectric vibrational angular velocity meter in accordance with thepresent invention will be explained with reference to FIGS. 51 and 52.FIG. 51 is a perspective view of this vibrator 1400, whereas FIG. 52 isa front view thereof.

In this vibrator 1400, PZT plates (i.e., piezoelectric elements) 1420,1430, and 1440 each of which has a length of 1.4 mm, a width of 3 mm,and a thickness of 0.3 mm with electrodes (not depicted) formed bysilver paste on both sides thereof are respectively bonded to three sidesurfaces of a metal pole (column) 1410 having an equilateral triangularcross section, whose each side is 2 mm, with a length of 15 mm. Thesizes of the respective portions should not be restricted to thosementioned above. As in the case of the metal pole 1310 of the vibrator1300 shown in FIG. 49, a metal material whose modules of elasticitychanges little with respect to temperature is preferable as the materialfor the metal pole 1410.

In the case of this vibrator 1400, the self-excitation circuits shown inFIGS. 32, 36, 37, and 38 may be used as well. The metal pole 1410, theouter electrodes of the PZT plates 1420 and 1430, and the outerelectrode of the PZT plate 1440 may be respectively used as theelectrode 1032, electrodes 1033 and 1034, and electrode 1035 of thevibrator 1020.

In the following, a still another example of the vibrator used in thepiezoelectric vibrational angular velocity meter in accordance with thepresent invention will be explained with reference to FIGS. 53 and 54.FIG. 53 is a perspective view of this vibrator 1500, whereas FIG. 54 isa front view thereof.

In this vibrator 1500, band-like electrodes 1520, 1530, 1540, 1550, and1560 are formed on the side surface of a PZT cylinder 1510 having adiameter of 2 mm and a length of 14 mm so as to extend in thelongitudinal direction thereof in parallel to each other as shown inFIG. 54. The sizes of the respective portions should not be restrictedto those mentioned above, however.

In the case of this vibrator 1500, the self-excitation circuits shown inFIGS. 32, 36, 37, and 38 may be used as well. The two electrodes 1550and 1540, the electrodes 1530 and 1560, and the electrode 1520 may berespectively used as the electrode 1032, electrodes 1033 and 1034, andelectrode 1035 of the vibrator 1020.

The vibrator used in the piezoelectric vibrational angular velocitymeter in accordance with the present invention should not be restrictedto the vibrators mentioned above. Also, though the foregoing embodimentsrefer to the cases where the self-excitation circuit in accordance withthe present invention is used for driving the vibrator of thepiezoelectric vibrational angular velocity meter in a self-excitationmanner, the self-excitation circuit of the present invention can be usedfor vibrating the vibrator of other apparatuses or the like in aself-excitation manner.

As explained in the foregoing, the above-mentioned piezoelectricvibrational velocity meter can stabilize the driving voltage regardlessof the mechanical and electrical unstableness of the vibrator, therebystabilizing the amplitude of the self-excited vibration of the vibratorwhile preventing the vibrator from abnormally oscillating at frequenciesother than the resonance frequency thereof.

In the following, a piezoelectric vibrational angular velocity meter inaccordance with another embodiment will be explained. A piezoelectricvibrational angular velocity meter utilizing normal and inversepiezoelectric effects comprises a vibrator, an excitation driving meansfor driving the vibrator in an excitation manner, and a detecting meansfor detecting Coriolis force generated due to a rotation of thevibrator, thereby detecting the Coriolis force generated due to therotation of the vibrator. The piezoelectric vibrational angular velocitymeter is adopted as angular velocity sensor, manual blurring sensor, andthe like and has a number of achievements.

FIG. 64 shows a comparative piezoelectric vibrational angular velocitymeter. This piezoelectric vibrational angular velocity meter comprises avibrator 2001. a self-excitation driving circuit 2002 for driving thevibrator 2001 in a self-excitation manner, and a detection circuit 2003for detecting, based on a signal from the vibrator 2001, the detectionsignal corresponding to Coriolis force acting on the vibrator 2001.

In the vibrator 2001, piezoelectric elements 2005, 2006, and 2007 eachof which has electrodes (not depicted) respectively formed on both sidesthereof are attached to respective side surfaces of a vibrationsubstrate 2004 formed as an equilateral triangular pole made of anelinvar alloy. The two piezoelectric elements 2005 and 2006 are used fordetection, whereas the remaining piezoelectric element 2007 is used fordriving.

The two input terminals of the detection circuit 2003 are respectivelyconnected to the piezoelectric elements 2005 and 2006. Also, the twoinput terminals of the self-excitation driving circuit 2002 arerespectively connected to the piezoelectric elements 2005 and 2006,while the output terminal thereof is connected to the piezoelectricelement 2007.

The self-excitation driving circuit 2002 is constituted by an addercircuit 2010 composed of two resistors 2008 and 2009; an invertingamplifier 2015 composed of an operational amplifier 2011 and resistors2012 to 2014; and a low-pass filter 2020 composed of two steps of RCfilters formed by resistors 2016 and 2017 and capacitors 2018 and 2019.

The output voltages from the piezoelectric elements 2005 and 2006 areadded together at the adder 2010 and then inversely amplified by theinverting amplifier 2015. The phase of thus amplified voltage isadjusted by the low-pass filter 2020 so as to be supplied to thepiezoelectric element 2007 as a driving voltage. Consequently, apositive feedback is provided so as to attain a loop gain of 1 orhigher, whereby the vibrator 2001 is driven in a self-excitation manner.

The detection circuit 2003 takes out the differential between the outputvoltages from the piezoelectric elements 2005 and 2006, for example, soas to attain the detection signal corresponding to the Coriolis forceacting on the vibrator 2001.

In this piezoelectric vibrational angular velocity meter, however, sinceonly the self-excitation driving circuit 2002 is used as an excitationdriving circuit for driving the vibrator 2001 in an excitation manner,the rise time after the self-excitation driving circuit 2001 is startedtill the amplitude of vibration of the vibrator 2001 attains ameasurable amplitude (stationary state) is long.

In particular, since the piezoelectric constant of the piezoelectricmaterial forming the vibrator 2001 is highly dependent on temperature,it greatly varies upon temperature in this piezoelectric vibrationalangular velocity meter. When the environmental temperature in use islow, for example, at a temperature not higher than 0° C., the rise timefor the vibrator 2001 becomes remarkably long.

Accordingly, in cases where this piezoelectric angular velocity meter2001 is used for measuring Coriolis force in real time, for example, inorder to detect manual blurring of a still camera and vibrations otherthan the manual blurring, a time lag may occur in the measured valuewhen the measurement is effected after the stationary state is attainedor reproducibility cannot be attained when the measurement is effectedbefore the stationary state is achieved. Accordingly, it has not beensuitable for the measurement in which a rapid rise time is required.

In FIG. 65, (a) shows the output waveform of the self-excitation drivingcircuit 2002 (i.e., state of vibration of the vibrator 2001) at roomtemperature (25° C.), whereas (b) shows that at a low temperature (0°C.). At room temperature, when started at time t₀, the amplitudegradually increases till time t₁ and becomes constant thereafter,thereby attaining a stationary state. At a low temperature, on the otherhand, the amplitude gradually increases till time t₂(>t₁) and becomesconstant thereafter, thereby attaining a stationary state. From FIG. 65,it can be seen that the rise time t₀ to t₂ of the vibrator 2001 at a lowtemperature is much longer than the rise time t₀ to t₁ of the vibrator2001 at room temperature.

In view of such circumstances, the following embodiments provideexcitation driving circuits and methods as well as piezoelectricvibrational angular velocity meters using the same by which the risetime for the vibrator can be reduced. First, the outline of theembodiments will be explained.

The excitation driving circuit of the first embodiment is an excitationdriving circuit for driving a vibrator in an excitation manner andcomprises a self-excitation driving circuit for driving the vibrator ina self-excitation manner and a forced excitation circuit CV for forciblydriving the vibrator PED1 when started.

The excitation driving circuit of the second embodiment furthercomprises, in the excitation driving circuit of the first embodiment, ameans by which, when an amplitude level of a signal indicative of thestate of vibration of the vibrator becomes a predetermined level orhigher, the excited driving of the vibrator by the forced excitationdriving circuit is nullified while only the excited driving of thevibrator by the self-excitation driving circuit is made effective.

The excitation driving circuit of the third embodiment furthercomprises, in the excitation driving circuit of the first embodiment, ameans by which, after a predetermined time has passed from the startingtime, the excited driving of the vibrator by the forced excitationdriving circuit is nullified while only the excited driving of thevibrator by the self-excitation driving circuit is made effective.

The excitation driving circuit of the fourth embodiment is an excitationdriving circuit for driving a vibrator in an excitation manner andcomprises a self-excitation driving circuit for driving the vibrator ina self-excitation manner and a pulse signal applying means for forciblyapplying a predetermined pulse to an input portion of theself-excitation driving circuit when started.

The excitation driving circuit of the fifth embodiment furthercomprises, in the excitation driving circuit of the fourth embodiment, ameans by which, when an amplitude level of a signal indicative of thestate of vibration of the vibrator becomes a predetermined level orhigher, the application of the pulse signal by the pulse signal applyingmeans is nullified.

The excitation driving circuit of the sixth embodiment furthercomprises, in the excitation driving circuit of the fifth embodiment, ameans by which, after a predetermined time has passed from the startingtime, the application of the pulse signal by the pulse signal applyingmeans is nullified.

The piezoelectric vibrational angular velocity meter of the seventhembodiment is a piezoelectric vibrational angular velocity metercomprising a vibrator and wherein the excitation driving circuit is thatin accordance with one of the first to sixth embodiments.

The excitation driving method in accordance with the eighth embodimentis an excitation driving method for driving a vibrator in an excitationmanner, wherein, after the vibrator is forcibly driven in an excitationmanner when started, the vibrator is driven in an self-excitationmanner.

According to the excitation driving circuits of the first to thirdembodiments of the present invention, while the vibrator is driven in aself-excitation manner by the self-excitation driving circuit, it isforcibly driven in an excitation manner by the forced excitation drivingcircuit when started. Accordingly, the rise time of the vibrator can bereduced as compared with the conventional cases. Therefore, Coriolisforce can be appropriately measured in real time in such cases asdetection of manual blurring of still camera or vibration other than themanual blurring.

Though the forced excited vibration of the vibrator by the forcedexcitation driving circuit is important for reducing the rise time ofthe vibrator when started, it is unnecessary and may rather deterioratethe self-excitation of the vibrator after the vibration of the vibratorhas reached its stationary state. Accordingly, it is preferable that,when the vibration of the vibrator attains the stationary state or astate in the proximity thereof, the excited driving of the vibrator bythe forced excitation driving circuit be nullified while the exciteddriving of the vibrator by the self-excitation circuit alone be madeeffective. In this case, the excited driving of the vibrator by theforced excitation driving circuit may be nullified while the exciteddriving of the vibrator by the self-excitation circuit alone is madeeffective when the amplitude level of the signal indicative of the stateof vibration of the vibrator is at a predetermined level or higher as inthe case of the excitation driving circuit of the second embodiment.Alternatively, the excited driving of the vibrator by the forcedexcitation driving circuit may be nullified while the excited driving ofthe vibrator by the self-excitation circuit alone is made effectiveafter a predetermined time has passed from the starting time as in thecase of the excitation driving circuit of the third embodiment.

Also, in the excitation driving circuits of the fourth to sixthembodiments, no forced excitation driving circuit is providedindependently from the self-excitation driving circuit. However, thepulse signal applying means applies a predetermined pulse signal to theinput portion of the self-excitation circuit when started. Due to thispredetermined pulse signal, the self-excitation driving circuit operatesas the forced excitation driving circuit. Namely, while a signal fromthe vibrator indicative of the state of vibration thereof is normallyapplied to the self-excitation driving circuit such that the vibrator isdriven by the self-excitation driving circuit in a self-excitationmanner, at the time of starting, the predetermined pulse signal is inputto the input portion of the self-excitation driving circuit such thatthe vibrator is forcibly excited by the self-excitation driving circuit.Accordingly, the rise time of the vibrator can be reduced by theexcitation driving circuits of the fourth to sixth embodiments as well.

Also, as mentioned above, the forced excited driving of the vibrator isunnecessary and may rather deteriorate the self-excitation of thevibrator after the vibration of the vibrator has reached its stationarystate. Accordingly, it is preferable that, when the vibration of thevibrator attains the stationary state or a state in the proximitythereof, the forced excited driving of the vibrator be nullified whilethe self-excited driving of the vibrator alone be made effective. Inthis case, the application of the pulse signal by the pulse signalapplying means may be nullified when the amplitude level of the signalindicative of the state of vibration of the vibrator is at apredetermined level or higher as in the case of the excitation drivingcircuit of the fifth embodiment. Alternatively, the application of thepulse signal by the pulse signal applying means may be nullified after apredetermined time has passed from the starting time as in the case ofthe excitation driving circuit of the sixth embodiment.

Also, according to the piezoelectric vibrational angular velocity meterof the seventh embodiment, since it has the excitation driving circuitof any of the first to sixth embodiments, the rising time of thevibrator is reduced. Accordingly, Coriolis force can be appropriatelymeasured in real time in such cases as detection of manual blurring ofstill camera or vibration other than the manual blurring.

Further, according to the excitation driving method of the eighthembodiment, since the vibrator is forcibly driven in an excitationmanner when started and then driven in a self-excitation manner, therise time for the vibrator can be reduced as in the case of theexcitation driving circuits of the first to sixth embodiments. In thefollowing, the foregoing embodiments of the present invention will beexplained in further detail with reference to the drawings.

In the following, the excitation driving circuits and methods as well asthe piezoelectric vibrational angular velocity meters using the samewill be explained in further detail with reference to the drawings.

FIG. 56 is a circuit diagram of a piezoelectric vibrational angularvelocity meter in accordance with an embodiment.

As shown in FIG. 56, this piezoelectric vibrational angular velocitymeter comprises a vibrator 1200, an excitation driving circuit 2031 fordriving the vibrator 1200 in an excitation manner, and a detectioncircuit 2032 which attains, based on an input signal from the vibrator1200, a detection signal corresponding to Coriolis force acting on thevibrator 1200.

First, the vibrator 1200 is shown in FIGS. 39 and 40. The configurationof the vibrator 1200 is identical to that of the vibrator PED1 shown inFIG. 1. In order for the vibrator 1200 to effectively vibrate uponapplication of a driving voltage thereto and to yield a large voltagegenerated due to the vibration thereof, a piezoelectric material havinga large Q value is selected as the material for each of the members 1030and 1031. Also, it is preferable for the vibrator 1200 to have resonancefrequencies in its thickness direction and width direction substantiallycoincide with each other. When they coincide with each other, thevertical cross section of the vibrator 1200 becomes substantiallysquare. For example, this frequency matching operation is effected as,while the vibrator 1200 is vibrated, its side surface is shaven withlaser or the like so as to adjust the resonance frequency.

With reference to FIG. 56 again, the two input terminals of thedetection circuit 2032 are respectively connected to the electrodes 1034and 1033. The detection circuit 2032 takes out the differential betweenthe output voltages from the electrodes 1033 and 1034, for example, toattain a detection signal corresponding to the Coriolis force acting onthe vibrator 1200. The detection circuit 2032 is configured, forexample, similarly to the conventional detection circuit.

Next, the excitation driving circuit 2031 will be explained withreference to FIG. 56.

The excitation driving circuit 2031 comprises a self-excitation drivingcircuit 2050 for driving the vibrator 1200 in a self-excitation mannerand a forced excitation circuit 2051 for forcibly driving the vibrator1200 in an excitation manner when started.

The input terminal of the self-excitation driving circuit 2050 isconnected to the electrode 1201 of the vibrator 1200, whereas the outputterminal of the self-excitation driving circuit 2050 is connected to theelectrode 1035 of the vibrator 1200 by way of an analog switch 2080 aswill be explained later. The self-excitation driving circuit 2050 isconstituted by an inverting amplifier 2064 composed of an operationalamplifier 2060 and resistors 2061 to 2063 and a low-pass filter 2069composed of two steps of RC filters comprising resistors 2065 and 2066and capacitors 2067 and 2068. The configuration of the self-excitationdriving circuit 2050 should not be restricted thereto, however. Theoutput voltage from the electrode 1201 is inversely amplified by theinverting amplifier 2064. The phase of thus amplified voltage isadjusted by the low-pass filter 2069. When the analog switch 2080 is on,thus phase-adjusted voltage is supplied to the electrode 1035 as adriving voltage by way of the analog switch 2080. As a result, apositive feedback is provided so as to attain a loop gain of 1 orhigher, whereby the vibrator 1200 is driven in a self-excitation manner.According to this self-excitation driving circuit 2050, simple harmonicoscillation of the vibrator 1200 with bending in the direction(thickness direction) perpendicular to the surfaces of the electrodes1034 and 1033 can be attained.

As mentioned previously, the electrode 1032 of the vibrator 1200 is usedas a reference electrode so as to be maintained at potentialV_(ref)(=V_(CC)/2, e.g., 2.5 V) by means of a power source circuit whichis not depicted. Here, V_(CC) indicates a power source voltage (e.g., 5V).

On the other hand, the forced excitation driving circuit 2051 isconstituted by an oscillation circuit comprising a Schmitt triggerinverter 2070, a resistor 2071, and a capacitor 2072. The configurationof the forced excitation driving circuit 2051 should not be restrictedthereto, however. When both of a power switch 2090 (corresponding to astart switch, contact, or the like in this embodiment) and an analogswitch 2080, which will be explained later, are on, the power sourcevoltage V_(CC) is supplied to the power source terminal of the Schmitttrigger inverter 2070 and thus the forced excitation driving circuit2051 performs an oscillating operation, whereby an oscillation outputpulse is attained from the output terminal of the Schmitt triggerinverter 2070. The values of the resistor 2071 and capacitor 2072 areselected such that the oscillation frequency substantially coincideswith the mechanical resonance frequency of the vibrator 1200. Also, theoutput terminal of the Schmitt trigger inverter 2070 (output terminal ofthe forced excitation driving circuit 2051) is connected to theelectrode 1035 of the vibrator 1200 by way of an analog switch 2082which will be explained later. When the analog switch 2082 is on, theoscillation output pulse is supplied to the electrode 1035 as a drivingvoltage by way of the analog switch 2082.

Further, as shown in FIG. 56, the excitation driving circuit 2031 hasthe analog switches 2080, 2081, and 2082, inverters 2083 and 2084, aresistor 2085, a capacitor 2086, and a diode 2087. In the analogswitches 2080, 2081, and 2082, the junctions between terminals 2080a and2080b, between 2081a and 2081b, and between 2082a and 2082b arerespectively turned on and off when high and low level signals areapplied to control terminals 2080c, 2081c, and 2082c, respectively.Between the output terminal of the self-excitation driving circuit 2050and the earth (0 V), the diode 2087, the resistor 2085, and thecapacitor 2086 are connected in series. Here, the resistor 2085 andcapacitor 2086 constitute an RC low-pass filter. The middle point(output terminal of the RC low-pass filter) in the connection betweenthe resistor 2085 and capacitor 2086 is connected to the input terminalof the inverter 2084. The output terminal of the inverter 2084 isconnected to the input terminal of the inverter 2083. The outputterminal of the inverter 2083 is connected to the control terminal 2080cof the analog switch 2080. The output terminal of the inverter 2084 isalso connected to the respective control terminals 2081c and 2082c ofthe analog switches 2081 and 2082.

In this embodiment, the analog switches 2080, 2081, and 2082, inverters2083 and 2084, resistor 2085, capacitor 2086, and diode 2087 constitutea means by which, when the amplitude level of a signal indicative of thestate of vibration of the vibrator 1200 becomes a predetermined level orhigher, the excited driving of the vibrator 1200 by the forcedexcitation driving circuit 2051 is nullified while the excited drivingof the vibrator 1200 by the self-excitation driving circuit 2050 aloneis made effective. Namely, by way of the diode 2087 and resistor 2085,the capacitor 2086 is charged with the output of the forced excitationdriving circuit 2051 as the signal indicative of the state of vibrationof the vibrator 1200. The charged voltage (output of the RC low-passfilter constituted by the resistor 2085 and capacitor 2086) correspondsto the amplitude level of the output of the self-excitation drivingcircuit 2050. Until the level of thus charged voltage reaches athreshold value V_(TH1) of the inverter 2084 (the level of the chargedvoltage being set so as to reach the threshold value V_(TH1) of theinverter 2084 when the output of the forced excitation driving circuit2051 substantially attains its stationary state, i.e., when thevibration of the vibrator 1200 substantially attains its stationarystate), the outputs of the inverter 2084 and 2083 are respectively setto high and low levels. Consequently, the analog switch 2080 is turnedoff, while the analog switches 2081 and 2082 are turned on, whereby theexcited driving of the vibrator 1200 by the forced excitation drivingcircuit 2051 is made effective while the excited driving of the vibrator1200 by the self-excitation driving circuit 2050 is nullified. Then,after the level of the charged voltage of the capacitor 2086 has reachedthe threshold value V_(TH1) of the inverter 2084, the outputs of theinverter 2084 and 2083 are respectively set to low and high levels.Consequently, the analog switch 2080 is turned on, while the analogswitches 2081 and 2082 are turned off, whereby the excited driving ofthe vibrator 1200 by the forced excitation driving circuit 2051 isnullified while the excited driving of the vibrator 1200 by theself-excitation driving circuit 2050 alone is made effective. Though theoutput of the self-excitation driving circuit 2050 is used as the signalindicative of the state of vibration of the vibrator 1200 in thisembodiment, the signal derived from the electrode 1201, for example, maybe used therefor as well.

Next, with reference to the timing chart shown in FIG. 57, the operationof the piezoelectric vibrational angular velocity meter in accordancewith this embodiment, in particular, that of the excitation drivingcircuit 2031, will be explained.

In FIG. 57, (a), (b), (c), (d), (e) and (f) show the on/off states ofthe power switch 2090, the on/off states of the analog switches 2081 and2082, the on/off states of the analog switch 2080, the output of theforced excitation driving circuit 2051, the output of theself-excitation driving circuit 2050, and the charged voltage of thecapacitor 2086, respectively.

First, at time t₁₀, the power switch 2090 is turned on so as to startthe apparatus ((a) in FIG. 57). At this point, since the vibration ofthe vibrator 1200 is not in its stationary state yet, the output of theself-excitation driving circuit 2050 is nearly zero, whereby the chargedvoltage of the capacitor 2086 is lower than the threshold value V_(TH1)of the inverter 2084 ((f) in FIG. 57). Accordingly, the analog switches2081 and 2082 are turned on ((b) in FIG. 57), while the analog switch2080 remains off ((c) in FIG. 57). Therefore, the forced excitationdriving circuit 2051 oscillates to output an oscillation output pulsehaving a frequency substantially identical to the resonance frequency ofthe vibrator 1200 ((d) in FIG. 57). This oscillation output pulse issupplied to the electrode 1035 of the vibrator 1200 by way of the analogswitch 2082, whereby the vibrator 1200 is forcibly vibrated with anamplitude which is relatively large even at the beginning and graduallyincreases. As a signal is obtained from the electrode 1201 of thevibrator 1200 in response to this vibration, the self-excitation drivingcircuit 2050 has an output such as that shown in (e) of FIG. 57. As aresult, the charged voltage of the capacitor 2086 gradually increases asshown in (f) of FIG. 57. Here, until the charged voltage of thecapacitor 2086 reaches the threshold value V_(TH1) of the inverter 2084,the analog switch 2080 remains off, whereby the output of theself-excitation driving circuit 2050 is not supplied to the electrode1035.

At time t₁₁ where the charged voltage of the capacitor 2086 has reachedthe threshold value V_(TH1) of the inverter 2084 (the vibrator beingsubstantially in its stationary state at this point in this embodiment),the analog switches 2081 and 2082 are turned off whereas the analogswitch 2080 is turned on. Accordingly, the forced excitation drivingcircuit 2051 stops its oscillating operation, while the output terminalof the inverter 2070 is separated from the electrode 1035. Also, theoutput of the self-excitation driving circuit 2050 is supplied to theelectrode 1035 by way of the analog switch 2080, whereby the vibrator1200 is driven in a self-excitation manner with the resonance frequencyof the vibrator 1200. As a result, as shown in (e) of FIG. 57, theamplitude of the vibrator 1200 becomes stable at time t₁₂ andthereafter, whereby the self-excited vibration of the vibrator 1200continues under its stationary state.

In this embodiment, at the starting (period t₁₀ to t₁₂), the vibrator1200 is forcibly driven in an excitation manner by the forced excitationdriving circuit 2051, whereby the rise time t₁₀ to t₁₂ for the vibrator1200 is greatly reduced as compared with conventional cases even whenthe environmental temperature in use changes.

Next, a piezoelectric vibrational angular velocity meter in accordancewith another embodiment will be explained with reference to FIGS. 58 and59.

FIG. 58 is a circuit diagram showing the piezoelectric vibrationalangular velocity meter in accordance with this embodiment. In FIG. 58,constituents identical or corresponding to those shown in FIG. 56 arereferred to with marks identical thereto without repeating theiroverlapping explanations.

The piezoelectric vibrational angular velocity meter of this embodimentdiffers from that shown in FIGS. 56 and 57 only in the configuration ofthe excitation driving circuit 2031. The excitation driving circuit 2031in FIG. 58 differs from that in FIG. 56 only in that the inverters 2083and 2084, resistor 2085, capacitor 2086, and diode 2087 in FIG. 56 areomitted while inverters 2101 and 2102, resistors 2103 and 2104, and acapacitor 2105 are provided instead as shown in FIG. 58.

In this embodiment, between a terminal of the power switch 2090 oppositeto the power source and the ground (0 V), the capacitor 2105 and theresistor 2103 are connected in series. Also, between the terminal of thepower switch 2090 opposite to the power source and the ground (0 V), theresistor 2104 used for discharge is connected. The middle point of theconnection between the capacitor 2105 and the resistor 2103 is connectedto the input terminal of the inverter 2102. The output of the inverter2102 is connected to the control terminal 2080c of the analog switch2080 and the input terminal of the inverter 2101. The output terminal ofthe inverter 2101 is connected to the respective control terminals 2081cand 2082c of the analog switches 2081 and 2082.

In this embodiment, the analog switches 2080, 2081, and 2082, inverters2101 and 2102, resistors 2103 and 2104, and capacitor 2105 constitute ameans by which, after a predetermined time has passed from the startingpoint, the excited driving of the vibrator 1200 by the forced excitationdriving circuit 2051 is nullified while the excited driving of thevibrator 1200 by the self-excitation driving circuit 2050 alone is madeeffective. Namely, when the power switch 2090 is turned on, an electriccurrent successively flows through the capacitor 2105 and the resistor2103 such that the capacitor 2105 is charged, whereby the voltage of theinput terminal of the inverter 2102 gradually decreases from the powersource voltage V_(CC) which is attained immediately after the powerswitch 2090 is turned on. Until the voltage of the input terminal of theinverter 2102 has reached a threshold value V_(TH2) of the inverter 2102(the level of the input terminal of the inverter 2102 being set so as toreach the threshold value V_(TH2) of the inverter 2102 when the outputof the forced excitation driving circuit 2051 substantially attains itsstationary state, i.e., when the vibration of the vibrator 1200substantially attains its stationary state) after a predetermined timewhich is determined by the time constants of the capacitor 2105 andresistors 2103 and 2104, the outputs of the inverter 2102 and 2101 arerespectively set to low and high levels. Consequently, the analog switch2080 is turned off, while the analog switches 2081 and 2082 are turnedon, whereby the excited driving of the vibrator 1200 by the forcedexcitation driving circuit 2051 is made effective while the exciteddriving of the vibrator 1200 by the self-excitation driving circuit 2050is nullified. Then, after the voltage of the input terminal of theinverter 2102 has reached the threshold value V_(TH2) of the inverter2102, the outputs of the inverter 2101 and 2102 are respectively set tolow and high levels. Consequently, the analog switch 2080 is turned on,while the analog switches 2081 and 2082 are turned off, whereby theexcited driving of the vibrator 1200 by the forced excitation drivingcircuit 2051 is nullified while the excited driving of the vibrator 1200by the self-excitation driving circuit 2050 alone is made effective.

Next, with reference to the timing chart shown in FIG. 59, the operationof the piezoelectric vibrational angular velocity meter in accordancewith this embodiment shown in FIG. 58, in particular, that of theexcitation driving circuit 2031, will be explained.

In FIGS. 59, (a), (b), (c), (d), (e) and (f) show the on/off states ofthe power switch 2090, the on/off states of the analog switches 2081 and2082, the on/off states of the analog switch 2080, the output of theforced excitation driving circuit 2051, the output of theself-excitation driving circuit 2050, and the voltage of the inputterminal of the inverter 2102, respectively.

First, at time t₂₀, the power switch 2090 is turned on so as to startthe apparatus ((a) in FIG. 59). At this point, since the capacitor 2105has not been charged yet, the input terminal of the inverter 2102 is atthe power supply voltage V_(CC) which is beyond the threshold valueV_(TH2) of the inverter 2102 ((f) in FIG. 59). Accordingly, the analogswitches 2081 and 2082 are turned on ((b) in FIG. 59), while the analogswitch 2080 remains off ((c) in FIG. 59). Therefore, the forcedexcitation driving circuit 2051 oscillates to output an oscillationoutput pulse having a frequency substantially identical to the resonancefrequency of the vibrator 1200 ((d) in FIG. 59). This oscillation outputpulse is supplied to the electrode 1035 of the vibrator 1200 by way ofthe analog switch 2082, whereby the vibrator 1200 is forcibly vibratedwith an amplitude which is relatively large even at the beginning andgradually increases. Then, as the capacitor 2105 is charged, the voltageat the input terminal of the inverter 2102 gradually decreases as shownin (f) of FIG. 59. Here, until the voltage of the input terminal of theinverter 2102 reaches the threshold value V_(TH2) of the inverter 2102,the analog switch 2080 remains off, whereby the output of theself-excitation driving circuit 2050 is not supplied to the electrode1035.

At time t₂₁ where the voltage at the input terminal of the inverter 2102has reached the threshold value V_(TH2) of the inverter 2102 (thevibrator being substantially in its stationary state at this point inthis embodiment) after a predetermined time has passed from the startingpoint t₂₀, the analog switches 2081 and 2082 are turned off whereas theanalog switch 2080 is turned on. Accordingly, the forced excitationdriving circuit 2051 stops its oscillating operation, while the outputterminal of the inverter 2070 is separated from the electrode 1035.Also, the output of the self-excitation driving circuit 2050 is suppliedto the electrode 1035 by way of the analog switch 2080, whereby thevibrator 1200 is driven in a self-excitation manner with the resonancefrequency of the vibrator 1200. As a result, as shown in (e) of FIG. 59,the amplitude of the vibrator 1200 becomes stable at time t₂₂ andthereafter, whereby the self-excited vibration of the vibrator 1200continues under its stationary state.

Also in this embodiment, at the starting (period t₂₀ to t₂₂), thevibrator 1200 is forcibly driven in an excitation manner by the forcedexcitation driving circuit 2051, whereby the rise time t₂₀ to t₂₂ forthe vibrator 1200 is greatly reduced as compared with theabove-mentioned comparative angular velocity meter even when theenvironmental temperature in use changes.

Next, a piezoelectric vibrational angular velocity meter in accordancewith another embodiment will be explained with reference to FIG. 60.

FIG. 60 is a circuit diagram showing the piezoelectric vibrationalangular velocity meter in accordance with this embodiment. In FIG. 60,constituents identical or corresponding to those shown in FIG. 56 arereferred to with marks identical thereto without repeating theiroverlapping explanations.

The piezoelectric vibrational angular velocity meter of this embodimentdiffers from that shown in FIGS. 56 and 57 only in the configuration ofthe excitation driving circuit 2031. The excitation driving circuit 2031of this embodiment differs from that in FIG. 56 only in that the analogswitches 2080 and 2082 and inverter 2083 in FIG. 56 are omitted while adiode 2110 is provided instead and that the output of self-excitationdriving circuit 2051 is directly connected to the electrode 1035 of thevibrator 1200 while the output of the circuit 2051 is connected to themiddle point of the connection between the input terminal of theself-excitation driving circuit and the electrode 2101 by way of thediode 2110.

In this embodiment, the circuit 2051 functions as a pulse signalapplying means for forcibly applying a predetermined pulse signal to theinput portion of the self-excitation driving circuit 2050 when started,while also being used as a forced excitation driving circuit. Namely,the oscillation output pulse from the circuit 2051 is also applied tothe input terminal of the self-excitation driving circuit 2050 by way ofthe diode 2110 so as to be used as the predetermined pulse signal. Also,the oscillation output pulse from the circuit 2051 is applied to theelectrode 1201 by way of the diode 2110 and used as a driving signal forforcibly driving the vibrator 1200 in an excitation manner. Here, thevibrator 1200 also vibrates when the driving signal is applied to theelectrode 1201. Accordingly, in this embodiment, when the oscillationoutput pulse is generated from the circuit 2051, this oscillation outputpulse is applied to the input terminal of the self-excitation drivingcircuit 2050. Then, the output of the self-excitation driving circuit2050 generated in response thereto is applied to the electrode 1035 ofthe vibrator 1200 so as to forcibly vibrate the vibrator 1200, while theoscillation output is applied to the electrode 1201 so as to forciblyvibrate the vibrator 1200. Here, when the oscillation output pulse fromthe circuit 2051 is applied to the input terminal of the self-excitationdriving circuit 2050, the self-excitation driving circuit 2050 operatesas the forced excitation driving circuit.

However, for example, a reverse-current preventing diode may be insertedso as to prevent the oscillation output pulse of the circuit 2051 frombeing applied to the electrode 1201 such that the circuit 2051 is merelyused as the pulse signal applying means without being used as the forcedexcitation driving circuit. In this case, the analog switch 2081,inverter 2084, resistor 2085, capacitor 2086, and diode 2087 constituteonly a means by which, when the amplitude level of a signal indicativeof the state of vibration of the vibrator 1200 becomes a predeterminedlevel or higher, the application of the pulse signal by the circuit 2051as the pulse signal applying means is nullified.

Next, the operation of the piezoelectric vibrational angular velocitymeter in accordance with this embodiment shown in FIG. 60, inparticular, that of the excitation driving circuit 2031, will beexplained. For this explanation, reference can be made to the timingchart shown in FIG. 57 (except for (c) thereof) as well.

First, at time t₁₀, the power switch 2090 is turned on so as to startthe apparatus ((a) in FIG. 57). At this point, since the vibration ofthe vibrator 1200 is not in its stationary state yet, the output of theself-excitation driving circuit 2050 is nearly zero, whereby the chargedvoltage of the capacitor 2086 is lower than the threshold value V_(TH1)of the inverter 2084 ((f) in FIG. 57). Accordingly, the analog switch2081 is turned on ((b) in FIG. 57). Therefore, the circuit 2051oscillates to output an oscillation output pulse having a frequencysubstantially identical to the resonance frequency of the vibrator 1200((d) in FIG. 57). This oscillation output pulse is supplied to theelectrode 1201 of the vibrator 1200 by way of the diode 2110. Also, thisoscillation output pulse is supplied to the input terminal of theself-excitation driving circuit 2050. The pulse generated at the outputterminal of the self-excitation driving circuit 2050 in response theretois supplied to the electrode 1035 of the vibrator 1200. As a result, dueto a synergetic effect of the pulses supplied to the electrodes 1201 and1035, the vibrator 1200 is forcibly vibrated with an amplitude which isrelatively large even at the beginning and gradually increases. As asignal is obtained from the electrode 1201 of the vibrator 1200 inresponse to this vibration, the self-excitation driving circuit 2050substantially has an output shown in (e) of FIG. 57. As a result, thecharged voltage of the capacitor 2086 gradually increases as shown in(f) of FIG. 57.

At time t₁₁ where the charged voltage of the capacitor 2086 has reachedthe threshold value V_(TH1) of the inverter 2084 (the vibrator beingsubstantially in its stationary state at this point in this embodiment),the analog switch 2081 is turned off. Accordingly, the forced excitationdriving circuit 2051 stops its oscillating operation. Therefore, theforced excitation of the vibrator 1200 is terminated, while the vibrator1200 is driven in a self-excitation manner by the output of theself-excitation driving circuit 2050 alone. As a result, as shown in (e)of FIG. 57, the amplitude of the vibrator 1200 becomes stable at timet₁₂ and thereafter, whereby the self-excited vibration of the vibrator1200 continues under its stationary state.

Also in this embodiment, at the starting (period t₁₀ to t₁₂), thevibrator 1200 is forcibly driven in an excitation manner, whereby therise time t₁₀ to t₁₂ for the vibrator 1200 is greatly reduced ascompared with the above-mentioned comparative angular velocity metereven when the environmental temperature in use changes.

Next, a piezoelectric vibrational angular velocity meter in accordancewith another embodiment will be explained with reference to FIG. 61.

FIG. 61 is a circuit diagram showing the piezoelectric vibrationalangular velocity meter in accordance with this embodiment. In FIG. 61,constituents identical or corresponding to those shown in FIG. 58 arereferred to with marks identical thereto without repeating theiroverlapping explanations.

The piezoelectric vibrational angular velocity meter of this embodimentdiffers from that shown in FIGS. 58 and 59 only in the configuration ofthe excitation driving circuit 2031. The excitation driving circuit 2031of this embodiment differs from that in FIG. 58 only in that the analogswitches 2080 and 2082 in FIG. 58 are omitted while a diode 2120 isprovided instead and that the output terminal of the self-excitationdriving circuit 2050 is directly connected to the electrode 1035 of thevibrator 1200 while the output of the circuit 2051 is connected to themiddle point of the connection between the input terminal of theself-excitation driving circuit and the electrode 1201 by way of thediode 2120.

In this embodiment, as in the case of the piezoelectric vibrationalangular velocity meter shown in FIG. 60, the circuit 2051 functions as apulse signal applying means for forcibly applying a predetermined pulsesignal to the input portion of the self-excitation driving circuit 2050when started, while also being used as a forced excitation drivingcircuit. Namely, the oscillation output pulse from the circuit 2051 isalso applied to the input terminal of the self-excitation drivingcircuit 2050 by way of the diode 2120 so as to be used as thepredetermined pulse signal. Also, the oscillation output pulse from thecircuit 2051 is applied to the electrode 1201 by way of the diode 2120and used as a driving signal for forcibly driving the vibrator 1200 inan excitation manner. Accordingly, in this embodiment, when theoscillation output pulse is generated from the circuit 2051, thisoscillation output pulse is applied to the input terminal of theself-excitation driving circuit 2050. Then, the output of theself-excitation driving circuit 2050 generated in response thereto isapplied to the electrode 1035 of the vibrator 1200 so as to forciblyvibrate the vibrator 1200, while the oscillation output is applied tothe electrode 1201 so as to forcibly vibrate the vibrator 1200. Here,when the oscillation output pulse from the circuit 2051 is applied tothe input terminal of the self-excitation driving circuit 2050, theself-excitation driving circuit 2050 operates as the forced excitationdriving circuit.

However, for example, a reverse-current preventing diode may be insertedso as to prevent the oscillation output pulse of the circuit 2051 frombeing applied to the electrode 1201 such that the circuit 2051 is merelyused as the pulse signal applying means without being used as the forcedexcitation driving circuit. In this case, the analog switch 2081,invertors 2101 and 2102, resistors 2103 and 2104, and capacitor 2105constitute only a means by which, after a predetermined time has passedfrom the starting point, the application of the pulse signal by thecircuit 2051 as the pulse signal applying means is nullified.

Next, the operation of the piezoelectric vibrational angular velocitymeter in accordance with this embodiment shown in FIG. 61, inparticular, that of the excitation driving circuit 2031, will beexplained. Also, in this explanation, reference can be made to thetiming chart shown in FIG. 59 (except for (c) thereof).

First, at time t₂o, the power switch 2090 is turned on so as to startthe apparatus ((a) in FIG. 59). At this point, since the capacitor 2105has not been charged yet, the input terminal of the inverter 2102 is atthe power supply voltage V_(CC) which is beyond the threshold value V ofthe inverter 2102 ((f) in FIG. 59). Accordingly, the analog switch 2081is turned on ((b) in FIG. 59). Therefore, the circuit 2051 oscillates tooutput an oscillation output pulse having a frequency substantiallyidentical to the resonance frequency of the vibrator 1200 ((d) in FIG.59). This oscillation output pulse is supplied to the electrode 1201 ofthe vibrator 1200 by way of the diode 2120. Also, this oscillationoutput pulse is supplied to the input terminal of the self-excitationdriving circuit 2050. The pulse generated at the output terminal of theself-excitation driving circuit 2050 in response thereto is supplied tothe electrode 1035 of the vibrator 1200. As a result, due to asynergetic effect of the pulses supplied to the electrodes 1201 and1035, the vibrator 1200 is forcibly vibrated with an amplitude which isrelatively large even at the beginning and gradually increases. Then, asthe capacitor 2105 is charged, the voltage at the input terminal of theinverter 2102 gradually decreases as shown in (f) of FIG. 59.

At time t₂₁ where the voltage of input terminal of the inverter 2102 hasreached the threshold value V_(TH2) of the inverter 2102 (the vibratorbeing substantially in its stationary state at this point in thisembodiment) after a predetermined time has passed from the startingpoint t₂₀, the analog switch 2081 is turned off. Accordingly, the forcedexcitation driving circuit 2051 stops its oscillating operation.Therefore, the forced excitation of the vibrator 1200 is terminatedwhile the vibrator 1200 is driven in a self-excitation manner by theoutput of the self-excitation driving circuit 2050 alone. As a result,as shown in (e) of FIG. 59, the amplitude of the vibrator 1200 becomesstable at time t₂₂ and thereafter, whereby the self-excited vibration ofthe vibrator 1200 continues under its stationary state.

Also in this embodiment, at the starting (period t₂₀ to t₂₂), thevibrator 1200 is forcibly driven in an excitation manner by the forcedexcitation driving circuit 2051, whereby the rise time t₂₀ to t₂₂ forthe vibrator 1200 is greatly reduced as compared with theabove-mentioned comparative angular velocity meter even when theenvironmental temperature in use changes.

Next, a piezoelectric vibrational angular velocity meter in accordancewith another embodiment will be explained with reference to FIGS. 62 and63.

FIG. 62 is a circuit diagram showing the piezoelectric vibrationalangular velocity meter in accordance with this embodiment. In FIG. 62,constituents identical or corresponding to those shown in FIG. 61 arereferred to with marks identical thereto without repeating theirexplanations.

The piezoelectric vibrational angular velocity meter of this embodimentdiffers from that shown in FIG. 61 only in the configuration of theexcitation driving circuit 2031. The excitation driving circuit 2031 ofthis embodiment differs from that in FIG. 61 only in that the circuit2051 and analog switch 2081 in FIG. 61 are omitted.

In this embodiment, a circuit composed of resistors 2103 and 2104 and acapacitor 2105 forms a forced excitation driving circuit CV, whilefunctioning as a pulse signal applying means for forcibly applying apredetermined pulse signal to the input portion of the self-excitationdriving circuit 2050 when started. Namely, when started, a single pulseis output from the middle point of the connection between the capacitor2105 and the resistor 2103. This single pulse is applied to theelectrode 1201 by way of the diode 2120 and used as a driving signal forforcibly driving the vibrator 1200 in an excitation manner. Also, thissingle pulse is applied to the input terminal of the self-excitationdriving circuit 2050 by way of the diode 2120 and used as thepredetermined pulse signal. Accordingly, in this embodiment, when thesingle pulse is generated, it is applied to the input terminal of theself-excitation driving circuit 2050. The output of the self-excitationdriving circuit 2050 generated in response thereto is applied to theelectrode 1035 of the vibrator 1200 so as to forcibly excite thevibrator 1200, while the oscillation output pulse is applied to theelectrode 1201 so as to forcibly excite the vibrator 1200.

Next, the operation of the piezoelectric vibrational angular velocitymeter in accordance with this embodiment shown in FIG. 62, inparticular, that of the excitation driving circuit 2031, will beexplained with reference to the timing chart shown in FIG. 63.

In FIG. 63, (a), (b), and (c) show the on/off states of the power switch2090, the voltage at the middle point of the connection between thecapacitor 2105 and the resistor 2103, and the output of theself-excitation driving circuit 2050, respectively.

First, at time t₃₀, the power switch 2090 is turned on so as to startthe apparatus ((a) in FIG. 63). The voltage at the middle point of theconnection between the capacitor 2105 and the resistor 2103 is at thepower supply voltage V_(CC) at this point and gradually decreasesthereafter ((b) in FIG. 63). Namely, when the power switch is turned on,a single pulse such as that shown in (b) of FIG. 63 is generated. Thissingle pulse is supplied to the electrode 1201 of the vibrator 1200 byway of the diode 2120. Also, this single pulse is supplied to the inputterminal of the self-excitation driving circuit 2050. Then, a pulsegenerated at the output terminal of the self-excitation driving circuit2050 in response thereto is supplied to the electrode 1035 of thevibrator 1200. As a result, due to a synergetic effect of the pulsessupplied to the electrodes 1201 and 1035, the vibrator 1200 is forciblyvibrated once initially with a relatively large amplitude when started.Thereafter, based on the signal from the electrode 1201 generated inresponse to this vibration, the self-excitation driving circuit 2050drives the vibrator 1200 in a self-excitation manner. As a result, asshown in (c) of FIG. 63, the amplitude of the vibrator 1200 becomesstable at time t₃₁ and thereafter, whereby the self-excited vibration ofthe vibrator 1200 continues under its stationary state.

Also in this embodiment, at the starting (initial part at the startingin this embodiment), the vibrator 1200 is forcibly driven in anexcitation manner by the forced excitation driving circuit, whereby therise time t₃₀ to t₃₁ for the vibrator 1200 is greatly reduced ascompared with the above-mentioned comparative angular velocity metereven when the environmental temperature in use changes.

Here, in the embodiments shown in FIGS. 56 to 62, the vibrator 1020shown in FIG. 43 may be used in place of the vibrator 1200 shown in FIG.39.

Also, in the embodiments shown in FIGS. 56 to 62, the vibrator 1020shown in FIG. 33 may be used in place of the vibrator 1200 shown in FIG.39.

When this vibrator 1020 is used, one terminal of the resistor 2061 maybe connected to the electrode 1033 or 1034 in FIGS. 56, 58, 60, 61, and62. Alternatively, to the self-excitation driving circuit 2050, tworesistors respectively corresponding to the resistors 2008 and 2009 inFIG. 64 may be added such that first ends of these two resistors arerespectively connected to the electrodes 1033 and 1034. For example, inthe case where the vibrator 1020 is used in FIG. 60, even when theabove-mentioned two resistors are added thereto, the cathode of thediode 2110 may be connected to the input terminal of the invertingamplifier 2064 of the self-excitation driving circuit 2050.

Also, in the embodiments shown in FIGS. 56 to 62, the vibrator 1210shown in FIG. 41 may be used in place of the vibrator 1200 shown in FIG.39.

Further, in the embodiments shown in FIGS. 56 to 62, the vibrator 1230shown in FIG. 45 may be used in place of the vibrator 1200 shown in FIG.39. In this case, the points connected to the electrode 1035 in FIGS.56, 58, 60, 61, and 62 are connected to the electrode 1231 of thevibrator 1230.

Also, in the embodiments shown in FIGS. 56 to 62, the vibrator 1240shown in FIG. 47 may be used in place of the vibrator 1200 shown in FIG.39.

Further, the vibrator 1300 shown in FIG. 49 may be used in place of thevibrator 1200 shown in FIG. 39 in the embodiments shown in FIGS. 56 to62. In this case, for example, the metal pole 1310, the outer electrodesof the PZT plates 1350 and 1340, and the outer electrode of the PZTplate 1320 may be respectively used as the electrode 1032, electrodes1033 and 1034, and electrode 1035 of the vibrator 1200. Also, to theself-excitation driving circuit 2050, two resistors respectivelycorresponding to the resistors 2008 and 2009 in FIG. 64 may be addedsuch that first ends of these two resistors are respectively connectedto the outer electrodes of the PZT plates 1350 and 1340.

Further, the vibrator 1400 shown in FIG. 51 may be used in place of thevibrator 1200 shown in FIG. 39 in the embodiments shown in FIGS. 56 to62. In this case, for example, the metal pole 1410, the outer electrodesof the PZT plates 1420 and 1430, and the outer electrode of the PZTplate 1440 may be respectively used as the electrode 1032, electrodes1033 and 1034, and electrode 1035 of the vibrator 1200. Also, to theself-excitation driving circuit 2050, two resistors respectivelycorresponding to the resistors 2008 and 2009 in FIG. 64 may be addedsuch that first ends of these two resistors are respectively connectedto the outer electrodes of the PZT plates 1420 and 1430.

Further, the vibrator 1500 shown in FIG. 51 may be used in place of thevibrator 1200 shown in FIG. 39 in the embodiments shown in FIGS. 56 to62. In this case, for example, the two electrodes 1550 and 1540, theelectrodes 1530 and 1560, and the electrode 1520 may be respectivelyused as the electrode 1032, electrodes 1033 and 1034, and electrode 1035of the vibrator 1200. Also, to the self-excitation driving circuit 2050,two resistors respectively corresponding to the resistors 2008 and 2009in FIG. 64 may be added such that first ends of these two resistors arerespectively connected to the electrodes 1530 and 1560.

In the following, a camera using such a self-excitation driving circuitwill be explained.

FIG. 66 shows a system configuration of a camera obtained when apiezoelectric vibrational angular velocity meter JY1 comprising anexcitation driving circuit, in which the self-excitation circuit shownin FIG. 32 and the forced excitation circuit CV shown in FIG. 62 arecombined together, is applied to the camera shown in FIG. 4A. Theconfiguration of a piezoelectric vibrational angular velocity meter JY2in FIG. 66 is identical to that of the angular velocity meter JY1. Theseangular velocity meters JY1 and JY2 are disposed such that thelongitudinal directions of their respective vibrators are perpendicularto each other as shown in FIG. 4A. Here, elements identical orequivalent to each other are referred to with identical marks withoutrepeating their overlapping explanations. Though the buffer amplifiers1071 and 1072 are not used in the system shown in FIG. 66, they may beincorporated therein.

A power source or battery BT accommodated within the camera supplies anelectric power to the system within the camera. As a shutter releasebutton 407 is pushed down, the camera performs an image capturingoperation. As the shutter release button 407 is pushed down, a switch 90is turned on, whereby a driving electric power is supplied to each ofthe angular velocity meters JY1 and JY2. Namely, as the shutter releasebutton 407 is pushed down, the potential of an input terminal 18cbecomes V_(CC). When the input voltage V_(CC) is applied to the inputterminal of the forced excitation circuit CV, namely, the joint betweenthe resistor 2103 and the capacitor 2105, one pulse of voltage isapplied to a center electrode 3 by way of the joint between the resistor2104 and the capacitor 2105 and then by way of the diode 2120.Accordingly, one pulse of voltage is applied between a ground electrode6 of the vibrator and the center electrode 3, whereby an upperpiezoelectric crystal layer 1 bends in its thickness direction. At thistime, the input pulse voltage transmitted through the diode 2120 is alsoapplied to the input terminal of the self-excitation circuit 1021.

The input pulse current which flows into the current/voltage convertingcircuit 1040 from the forced excitation circuit CV in response to theinput pulse voltage is converted into a pulse voltage. Thus convertedpulse voltage is input into the comparator 1041 from which the componentof this voltage greater than zero level is output as the high level. Theamplitude of the square wave voltage output from the comparator 1041 isadjusted by the potential dividing circuit 1042. The square wave voltagetransmitted through the potential dividing circuit 1042 is transmittedthrough the band-pass filter 1043 so as to be converted into a sine wavevoltage. The sine wave voltage output from the band-pass filter 1043 isinput into the phase shifter 1044.

The phase shifter 1044 adjusts the phase of the input voltage such thatthe phase of the sine wave voltage output therefrom equals to the phaseof the input voltage of the self-excitation circuit 1021. Accordingly,the pulse voltages are applied between the center electrode 3 and groundelectrode 6 of the vibrator and between the lower surface electrode 9and ground electrode 6 of the vibrator from the forced excitationcircuit CV and the self-excitation circuit 1021, respectively, wherebythe vibrator greatly bends in its thickness direction. Therefore, therise time for the vibrator can be reduced. Also, a voltage due to apiezoelectric effect is generated between the center electrode 3 andground electrode 6 of the upper piezoelectric crystal layer 1 which hasbent in the thickness direction. This voltage is input into theself-excitation circuit 1021 again, whereby the vibration of thevibrator continues. When the vibrator rotates while vibrating, Coriolisforce is imparted to the vibrator, thereby warping the vibration of thevibrator.

At each of left and right electrodes 4 and 5 of the vibrator, an ACvoltage, in which the voltage generated by the Coriolis force issuperposed on the voltage generated by the vibration, is generated. Thealternating currents flowing through the vibrator due to these ACvoltages are converted into AC voltages by current/voltage convertingcircuits 1080a and 1080b, respectively. The current/voltage convertingcircuits 1080a is constituted by an operational amplifier 1082a, aresistor 1083a, and a capacitor 1084a; whereas the current/voltageconverting circuits 1080b is constituted by an operational amplifier1082b, a resistor 1083b, and a capacitor 1084b. A differential amplifier558 outputs the difference between these AC voltages, namely, thevoltage component generated in response to the Coriolis force. Assumingthat the angular velocity is Ω and the velocity of vibration of thevibrator in its thickness direction is V, Coriolis force F is inproportion to Ω×V. At the time when the velocity of vibration V ismaximized, namely, when the vibrator is at the neutral position (phaseof vibration =0°), the Coriolis force F is maximized and, accordingly,the sine wave voltage (phase of AC voltage =90°) generated by theCoriolis force is also maximized.

Consequently, the phase of the electric signal corresponding to theCoriolis force output from the differential amplifier 558 is shiftedfrom the phase of the AC signal for vibrating the vibrator by about 90°.A phase shifter 562 makes the phases of these signals coincide with eachother. A multiplier 559 synchronously detects and then outputs themultiplication of these signals, namely, the voltage signalcorresponding to the Coriolis force output from the differentialamplifier 558. This voltage signal corresponding to the Coriolis forceis smoothed by the low-pass filter 560. Then, its gain is adjusted by again adjustment amplifier 561. Subsequently, it is digitized by an A/Dconverter 501 so as to be input into a central processing unit 502within the camera as an angular velocity data (X axis). Theconfiguration of the angular velocity meter JY2 is identical to that ofthe angular velocity meter JY1. The signal output from the angularvelocity meter JY2 is digitized by the A/D converter 501 so as to beinput into the central processing unit 502 within the camera as anangular velocity data (Y axis). Based on thus detected angular velocitydata, the central processing unit 502 controls motors 401 and 402 so asto move an image pickup lens 404. Here, the central processing unit 502moves the lens 404 as explained with reference to FIGS. 4B to 4D.

The vibrator used in the piezoelectric vibrational angular velocitymeter in accordance with the present invention should not be restrictedto the foregoing vibrators. Any of the foregoing vibrators orpiezoelectric vibrational angular velocity meters can be applied to theabove-mentioned camera. The excitation driving circuit can also be usedwhen vibrators of other apparatuses and the like are driven in anexcitation manner.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

The basic Japanese Application Nos. 207080/1994 (6-207080) filed on Aug.31, 1994, 207081/1994 (6-207081) filed on Aug. 31, 1994, 207082/1994(6-207082) filed on Aug. 31, 1994, 115693/1995 (7-115693) filed on May15, 1995, 170152/1995 (7-170152) filed on Jun. 13, 1995, and 209242/1995(7-209242) filed on Jul. 25, 1995 are hereby incorporated by reference.

1. An angular velocity meter comprising: a vibrator and aself-excitation driving circuit for driving said vibrator in aself-excitation manner, said self-excitation driving circuit comprising:a converting means for converting a first sine wave voltage indicativeof a state of vibration of said vibrator into a square wave voltagewhich becomes a first predetermined level when said first square sinewave voltage is greater than a predetermined reference level whilebecoming a second predetermined level when said first square sine wavevoltage is smaller than said predetermined reference level; a filter forfiltering a second sine wave voltage, which has a frequency identical toa frequency of said first sine wave voltage, from said square wavevoltage; and a phase shifter for adjusting a phase of said second sinewave voltage, which has been filtered by said filter, such that anamplitude of vibration of said vibrator is substantially maximized.
 2. Ameter according to claim 1, further comprising a current/voltageconverter which receives one input signal from said vibrator as anelectric current signal and converts said electric current signal into avoltage signal, said converting means converting an output of saidcurrent/voltage converter, as said first sine wave voltage, into saidsquare wave voltage.
 3. A meter according to claim 1, further comprisinga means for receiving one input signal from said vibrator as a voltagesignal, said converting means converting said voltage signal, as saidfirst sine wave voltage, into said square wave voltage.
 4. A meteraccording to claim 1, wherein said converting means includes azero-cross comparator.
 5. A meter according to claim 4, wherein saidconverting means further includes an attenuator for attenuating anoutput of said zero-cross comparator.
 6. A meter according to claim 5,wherein said attenuator comprises a potential dividing circuit includinga variable resistor.
 7. A meter according to claim 1, wherein saidvibrator comprises: a first piezoelectric crystal layer; at least threeelectrodes formed on an upper surface of said first piezoelectriccrystal layer; and an electrode formed on a lower surface of said firstpiezoelectric crystal layer.
 8. A camera comprising the meter accordingto claim
 1. 9. A self-excitation circuit for driving a vibrator in aself-excitation manner, said self-excitation circuit comprising: aconverting means for converting a first sine wave voltage indicative ofa state of vibration of said vibrator into a square wave voltage whichbecomes a first predetermined level when said first square sine wavevoltage is greater than a predetermined reference level while becoming asecond predetermined level when said first square sine wave voltage issmaller than said predetermined reference level; a filter for filteringa second sine wave voltage, which has a frequency identical to afrequency of said first sine wave voltage, from said square wavevoltage; and a phase shifter for adjusting a phase of said second sinewave voltage, which has been filtered by said filter, such that anamplitude of vibration of said vibrator is substantially maximized. 10.A self-excitation circuit according to claim 9, wherein said convertingmeans includes a zero-cross comparator.